The predictive value of primary tumor location in patients with metastatic colorectal cancer: A systematic review

Accepted Manuscript Title: The predictive value of primary tumor Please check the doc head and correct if necessary.–>location in patients with metastatic colorectal cancer: A systematic review Authors: Nele Boeckx, Katleen Janssens, Guy Van Camp, Marika Rasschaert, Konstantinos Papadimitriou, Marc Peeters, Ken Op de Beeck PII: DOI: Reference:

S1040-8428(17)30309-8 https://doi.org/10.1016/j.critrevonc.2017.11.003 ONCH 2450

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The predictive value of primary tumor location in patients with metastatic colorectal cancer: a systematic review Nele Boeckxa,b,*, Katleen Janssensa,*, Guy Van Campa,b, Marika Rasschaertc, Konstantinos

a

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Papadimitriouc, Marc Peetersa,c, Ken Op de Beecka,b

Center of Oncological Research (CORE), University of Antwerp, Universiteitsplein 1, 2610 Wilrijk,

Belgium

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b

Center of Medical Genetics, University of Antwerp and Antwerp University Hospital, Prins

Boudewijnlaan 43/6, 2650 Edegem, Belgium

Department of Oncology, Antwerp University Hospital, Wilrijkstraat 10, 2650 Edegem, Belgium

these authors contributed equally to this manuscript

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*

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c

e-mail addresses:

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[email protected]

[email protected]

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[email protected] [email protected]

[email protected]

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[email protected]

[email protected]

Beeck, Prins Boudewijnlaan 43/6, 2650

Edegem,

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Corresponding author: Ken Op de

[email protected], telephone number: 0032 3 275 97 91, fax: 0032 3 275 97 23

Abstract Colorectal cancer (CRC) is one of the most frequently diagnosed cancers worldwide. It has been reported that left- and right-sided CRC harbor varying disease characteristics, which leads to a 1

difference in prognosis and response to therapy. Recently, there have been retrospective studies about tumor location in metastatic CRC (mCRC) and its potential to predict the effect of anti-vascular endothelial growth factor and anti-epidermal growth factor receptor (anti-EGFR) therapies. In this review, we provide a comprehensive overview of the latest trials studying the predictive value of primary tumor location in mCRC and discuss biomarkers that might be associated with the differences in treatment response. Although data need to be interpreted with caution due to the absence of randomized trials stratified based on tumor location, patients with left-sided CRC seem to

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benefit more from anti-EGFR therapy than patients with right-sided CRC. Further clinical trials, stratified for tumor location, are warranted.

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Key words:

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Primary tumor location, predictive value, anti-EGFR therapy, anti-VEGF therapy, biomarkers

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Introduction

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Colorectal cancer (CRC) is the third most frequently diagnosed cancer accounting for 1.36 million new patients and 694,000 deaths worldwide, in 2012 [1]. During the last years, the impact of primary

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tumor location in CRC has been intensively studied by multiple research groups demonstrating varying disease characteristics in left- and right-sided CRC [2-19]. An overview of tumor features

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according to primary tumor location is shown in Table 1.

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The division in the right and left part of the colon is based on its embryological origin. The right part of the colon originates from the midgut, while the left part is derived from the hindgut. The embryological border between both parts of the colon is located at the proximal two-thirds of the

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transverse colon [24]. However, most researchers use the splenic flexure as the demarcation line between left- and right-sided tumors. In this way, the right part includes the appendix, caecum, ascending colon, hepatic flexure and transverse colon, while the left part consists of the splenic

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flexure, descending colon, sigmoid and rectum. However, in some studies, tumors of the transverse colon are excluded since classifying them as right-sided is not entirely correct [25]. Similarly, some authors classify rectal cancers as a third separate group and therefore exclude rectal cancers from left-sided CRC [26]. However, Price et al. (2015) reported similar outcomes for left-sided colon cancer and rectal cancer and suggested that combined analyses are appropriate [27]. Various studies have convincingly shown that patients with tumors originating on the left side of the colon have a significantly better prognosis (overall survival (OS), progression-free survival (PFS) and 2

disease-free survival) than those with tumors originating on the right side of the colon in all CRC stages [15, 16, 25, 27-35]. Therefore, tumor location has a prognostic value in CRC as it provides information about the overall cancer outcome, independent of treatment received. The predictive value on the other hand, provides information on the likelihood of response to a given therapy, and therefore helps to optimize treatment decisions [36, 37]. Recently, different research groups have studied the predictive value of tumor location in metastatic CRC (mCRC). Many investigators have turned to retrospective subgroup analysis to determine the

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potential of primary tumor location in predicting the effect of anti-vascular endothelial growth factor

(anti-VEGF) and anti-epidermal growth factor receptor (anti-EGFR) therapies. However, comparison of study results is hampered by heterogeneity in treatment and limited information on molecular

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and pathological features, so no formal conclusions could be drawn yet.

Although tumor sidedness is a subject that is currently undergoing intense study, a recent systematic review to provide an overview of the latest developments in this field is lacking. Therefore, the aim of

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this review is to provide a comprehensive overview of the latest trials studying the predictive value of primary tumor location in mCRC and discuss biomarkers that might be associated with the difference

2. Methods 2.1 Literature search

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in response to treatment.

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This systematic review is based on a comprehensive search of two databases (Medline and Web of Science) using several combinations of the following search terms: colorectal cancer, tumor sidedness, (primary) tumor location, right-sided, left-sided, proximal, distal, predictive, cetuximab,

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panitumumab, bevacizumab, anti-EGFR, anti-VEGF, biomarker, microbiota, biofilm and microbiome. Articles published in English between January 1, 2010 and June 1, 2017 were included. Articles were

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selected first based on abstract and subsequently based on full-text. The reference lists of the included articles were searched to identify other relevant studies that were missed with the first search strategy. Furthermore, important oncological conferences such as the American Society of

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Clinical Oncology and European Society for Medical Oncology were also searched.

2.2 Data interpretation Ideally, the predictive value of tumor location would be determined using an interaction test. Unfortunately, these data are not available for every study. Therefore, we report the available data and compare the data of patients with left-sided and right-sided tumors. In addition, these studies are all unplanned retrospective studies. None of the presented studies were randomized for tumor location, none of the analyses were pre-specified. In addition, sample 3

sizes for patients with right-sided tumors are small, so these data must be regarded as purely hypothesis generating.

3. Predictive value of tumor location Different recent studies have addressed the predictive value of tumor sidedness in mCRC. However, no consensus has been made yet. Hence, the most important trials studying the predictive value of

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tumor location regarding targeted therapies will be discussed here (Table 2).

3.1 Anti-EGFR therapy

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3.1.1 Chemotherapy versus chemotherapy plus anti-EGFR therapy In the retrospective analysis of the first-line CRYSTAL study, the addition of cetuximab to FOLFIRI significantly improved PFS, OS and objective response rate (ORR) among patients with RAS wild type

(wt) left-sided tumors. In contrast, only limited benefit in terms of PFS, OS and ORR was observed

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upon the addition of cetuximab to FOLFIRI in patients with right-sided tumors. However, cautious interpretation of right-sided data is required due to small sample sizes [31]. Similarly, in a

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retrospective analysis of the first-line PRIME trial, patients with left-sided tumors benefitted from the

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addition of panitumumab to FOLFOX compared to FOLFOX alone, indicated by significantly longer

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median OS and PFS, whereas no significant differences in median OS or PFS were observed in patients with right-sided mCRC. However, in both left- and right-sided tumors, the response rate (RR) was higher and the duration of response (DoR) was longer in the panitumumab arm compared to the

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FOLFOX alone arm [38]. These results are in line with the conclusion of the TAILOR trial where the addition of cetuximab to first-line FOLFOX significantly improved the outcome in terms of PFS, OS

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and ORR in RAS wt patients with left-sided mCRC. However, in patients with right-sided tumors, their data suggested a non-significant trend in favor of the addition of cetuximab regarding PFS and ORR

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[39]. Wang et al. (2015) reported that adding cetuximab to chemotherapy in both first- and secondline therapy significantly improved PFS, OS and ORR in patients with left-sided mCRC but limited benefit was observed in patients with right-sided tumors [33]. This corresponds to the findings of the 20050181 study, a second-line trial comparing FOLFIRI and FOLFIRI plus panitumumab in RAS wt

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mCRC. In this trial, the addition of panitumumab to FOLFIRI resulted in numerically improved median OS and PFS compared to FOLFIRI alone in patients with left-sided primary tumors. However, in patients with right-sided mCRC, the hazard ratio (HR) for PFS favored the panitumumab arm, while the HR for OS favored the FOLFIRI alone arm. Again, sample sizes for right-sided CRC were rather small and thus of limited value in terms of interpretation [40].

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3.1.2 Best supportive care versus anti-EGFR therapy In the 20020408 study, the addition of panitumumab to best supportive care (BSC) led to a significant benefit in PFS and an improved RR compared to BSC alone in patients with left-sided tumors. However, no difference in PFS between both treatment arms was observed in patients with rightsided tumors [40]. Similarly, in the retrospective analysis of the NCIC CO.17 trial, it was observed that the addition of cetuximab to BSC in patients with KRAS wt chemotherapy-refractory mCRC resulted in a significant benefit in PFS and OS in individuals with left-sided tumors. Although no difference in PFS

cetuximab arm. Again, sample sizes for right-sided CRC were rather small [41].

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3.2 Anti-VEGF therapy

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was detected in patients with right-sided tumors, there was a trend towards better OS in the

3.2.1 Chemotherapy versus chemotherapy plus anti-VEGF therapy Loupakis et al. (2015) studied the data sets from two large phase III studies (AVF2107g and NO16966) of first-line chemotherapy with or without bevacizumab. In this trial, right-sided location

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was a negative prognostic variable, independent of mucinous histology and BRAF mutational status.

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No association was detected for primary tumor location and bevacizumab efficacy as patients with both left- and right-sided CRC seemed to benefit from the addition of bevacizumab [15]. In addition,

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no difference in bevacizumab effect between left- and right-sided CRC was reported after re-analysis

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of the MAX trial comparing capecitabine vs capecitabine plus bevacizumab (+/- mitomycin C) [45]. These results were in contrast with the findings of He et al. (2017) who evaluated the predictive

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value of primary tumor location on bevacizumab effectiveness in a retrospective analysis. Their data showed that left-sided colon cancer patients in the bevacizumab arm had significantly longer OS compared to those in the chemotherapy alone arm. However, patients with right-sided colon cancer

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had similar OS when bevacizumab was added to standard chemotherapy. Significantly longer OS results were also detected in rectal cancer patients in the bevacizumab arm. Based on these findings,

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the authors concluded that only patients with left-sided CRC could obtain survival benefit from the addition of bevacizumab to first-line chemotherapy [42]. In the cohort-based trial by Boisen et al. (2013), the addition of bevacizumab to CAPEOX compared to CAPEOX monotherapy as first-line mCRC treatment improved OS in patients who had their primary tumor originating in the rectum and

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sigmoid colon [46]. Given the retrospective design of both studies which might lead to imbalances in patients’ baseline characteristics, these results should be considered hypothesis-generating with the need of further validation. The effect of tumor location on ramucirumab, another type of anti-VEGF therapy, was investigated by Portnoy et al. (2017). They reported that ramucirumab treatment enhanced median OS and PFS in

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both left- and right-sided CRC patients. Even though left-sided CRC patients had longer OS and PFS, they could not confirm sidedness as being predictive of ramucirumab efficacy [43].

3.3 Anti-EGFR versus anti-VEGF therapy In the retrospective analysis of the FIRE-3 study, RAS wt patients with left-sided tumors treated with FOLFIRI plus cetuximab had significantly longer OS than patients receiving FOLFIRI plus bevacizumab. However, there was no significant difference in ORR or PFS. In contrast, among patients with right-

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sided tumors, no significant differences in ORR, PFS or OS were observed. Nevertheless, cautious interpretation of data of right-sided tumors is required due to limited sample sizes [31]. Similarly, in the retrospective analysis of the PEAK study, patients with left-sided primary tumors in the

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panitumumab arm had numerically better median OS and PFS compared to patients in the

bevacizumab arm. In patients with right-sided tumors, the HR for OS favored panitumumab, while the HR for PFS favored bevacizumab. Again, the right-sided comparison was based on very few patients and should be evaluated with caution. Furthermore, in patients with both left- and right-

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sided tumors, a higher RR was seen for panitumumab versus bevacizumab. Longer median DoR was

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seen for the panitumumab arm compared to the bevacizumab arm in patients with left-sided tumors, while no difference was seen in right-sided disease [38]. Lu et al. (2016) studied the impact of

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primary tumor location in KRAS exon 2 wt mCRC patients treated with FOLFOX or FOLFIRI combined

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with either cetuximab or bevacizumab. In left-sided tumors, the cetuximab group reached higher ORR and numerically longer PFS and OS compared to the bevacizumab group. However, similar to

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the findings of the PEAK trial, contradicting results were observed in right-sided tumors; although the bevacizumab group had numerically longer PFS and OS, the cetuximab group had higher ORR [30]. Sagawa et al. (2017) investigated the impact of primary tumor location in mCRC patients receiving

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first-line chemotherapy in combination with either cetuximab or bevacizumab. In patients with leftsided tumors, the cetuximab group was significantly superior to the bevacizumab group in terms of

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OS. Conversely, in patients with right-sided tumors, the OS was higher in the bevacizumab group. However, this difference did not reach statistical significance, possibly due to small sample sizes [44]. In addition, the subgroup analysis of the CALGB/SWOG 80405 trial showed that OS was significantly longer in KRAS wt patients with left-sided tumors treated with first-line chemotherapy plus

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cetuximab compared to those receiving chemotherapy plus bevacizumab, whereas in right-sided disease, the addition of bevacizumab was superior to the addition of cetuximab [25]. These conclusions, although coming mostly from unplanned analysis on data from earlier randomized trials, are certainly interesting and may impact sequence-of-treatment decisions but warrant prospective validation before integrated in clinical practice.

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3.4 Pooled analyses A recent meta-analysis of the PRIME and CRYSTAL trial demonstrated that the patients with leftsided RAS wt tumors received greater benefit from anti-EFGR therapy than patients with right-sided tumors. When comparing anti-EGFR therapy to anti-VEGF therapy (CALGB/SWOG 80405, FIRE-3, PEAK), patients with left-sided tumors had greater survival benefit when treated with anti-EGFR therapy [28]. Another recent pooled analysis was performed based on data from the randomized CRYSTAL, PRIME,

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PEAK, FIRE-3, CALGB/SWOG 80405 and 20050181 trials. The predictive value of tumor location was

determined by comparing outcome in patients with right-sided or left-sided RAS wt tumors by using the hazard ratios and odds ratios in both treatment arms. The treatment arm containing anti-EGFR

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therapy was compared to the treatment arm containing chemotherapy alone or chemotherapy plus

bevacizumab. This analysis reported again a benefit in patients with left-sided RAS wt tumors treated with chemotherapy plus anti-EGFR therapy which was not present in patients with right-sided tumors

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[47].

4. Biomarkers

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The complex molecular mechanisms causing the difference in clinical presentation and response to

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therapy of right-sided and left-sided CRC still remain unclear. In the following section, we provide an overview of biomarkers that are differently expressed according to tumor location which might be

summarized in Table 3.

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4.1 Gut content

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associated to these differences. An overview of the varying biomarkers is shown in Figure 1 and

The microbiome aids in regulating the homeostasis and health of the gut. Dysbiosis, a state of imbalance in the microbiome, is associated with the development of CRC [48]. It has been suggested

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that the difference in colonic microbiota between the left and right side of the colon may contribute to the difference in etiology, clinical behavior and prognosis of left- and right-sided CRC. A high amount of Fusobacterium nucleatum DNA in CRC tissue (measured using a quantitative PCR assay) is

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associated with right-sided tumor location [49, 50]. The proportion of CRC with a high-level of Fusobacterium nucleatum gradually increased linearly along the large intestine from rectal cancers to caecal cancers [49]. Furthermore, the left part of the colon has a higher bacterial load than the right part, resulting in more fermentation and consequently short-chain fatty acid production. In addition, there is a difference in exposure to mutagenic metabolites; higher levels are observed in the left colon

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compared to the right colon. However, this difference might be balanced by the increased exposure to carcinogenic bile acids and their metabolites in the right part of the colon [51]. Biofilms are dense aggregations of bacteria that adhere to either biological or non-biological surfaces. Biofilms invading the colonic mucus layer and creating direct contact with mucosal epithelial cells indicate a pathologic state. In a study of Dejea et al. (2014), invasive polymicrobial biofilms were detected on almost all right-sided tumors, while it was only present on 12% of leftsided tumors. In addition, bacterial biofilms were associated with various features of oncogenic

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transformation, such as loss of E-cadherin, increased levels of the angiogenic and pro-inflammatory cytokine IL-6, as well as activation of the downstream effector STAT3 and increased epithelial crypt

cell proliferation [52]. In another publication of the same research group, it was reported that N1,N12-

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diacetylspermine was significantly upregulated in tissues with biofilms. N1,N12-diacetylspermine is a

pro-proliferative polyamine metabolite that may affect the growth of both cancer and its associated biofilms [53]. In contrast, in a study of Yu et al. (2016), bacterial biofilms were observed on 52.1% of

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right-sided CRCs and on 55.6% of left-sided CRCs [50]. This discrepancy creates difficulties in the understanding of the role of Fusobacterium nucleatum invasion into tumor tissues and needs further

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validation.

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4.2 Genomic instability

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Microsatellite instability (MSI) and its associated hypermutability, results from impaired DNA mismatch repair (MMR). Previous research has established that MSI-high tumors are more frequently

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observed on the right side of the colon [54-59]. Moreover, the frequency of MSI-high tumors gradually increased from rectum to ascending colon [60]. This corresponds to the fact that deficient MMR status was significantly associated with right-sided tumor location [23, 61]. Similarly, the large

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genome-scale analysis of CRC samples carried out by the Cancer Genome Atlas Network, reported that right-sided cancers were more frequently hypermutated [62]. In addition, a recent re-analysis of

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the CALGB/SWOG 80405 trial revealed no difference in OS between the bevacizumab and cetuximab arm for patients with microsatellite stable tumors (32.6 vs. 30.1 months), while a large benefit in the bevacizumab arm was observed in MSI-high tumors (30.0 vs 11.2 months). As MSI-high tumors are predominantly present in patients with right-sided tumors, this finding may reflect the negative

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impact of anti-EGFR therapy in patients with right-sided disease [63]. In contrast to tumors with MSI, tumors with chromosomal instability were more frequently located on the left side [9, 55, 64].

4.3 Epigenetic alterations 4.3.1 CpG island methylator phenotype The CpG island methylator phenotype (CIMP) was first introduced by Toyota et al. (1999) to describe CRC with hypermethylation of multiple CpG island loci [65]. Hypermethylation of promoter region 8

CpG islands can cause epigenetic inactivation of tumor suppressor genes which can result in the development of malignancies. It has been reported in various studies that CIMP-positive status is significantly associated with right-sided tumor location [9, 54, 55, 60, 62, 65-76]. Approximately 30–40% of sporadic right-sided colon cancers are CIMP-positive, compared to 3–12% of left-sided colon and rectal cancers [77]. In line with these findings, two meta-analyses concluded that CIMPpositive CRC displayed a significant association with right-sided location [57, 75]. Moreover, the

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frequency of CIMP-high tumors gradually increased from rectum to ascending colon [60, 68]. 4.3.2 LINE–1 methylation Long interspersed nucleotide element-1 (LINE-1) are transposable elements in the DNA. In the meta-

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analysis of Tang et al. (2015) it was reported that LINE-1 methylation levels in right-sided colon cancer were significantly higher than in left-sided colon cancer [78]. Furthermore, a pattern in LINE-1 methylation level was observed; the methylation level gradually decreased from rectum to descending colon and then increased from descending colon to ascending colon [60, 79].

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4.4 Consensus molecular subtypes classification

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In order to develop a universal molecular classification of colorectal cancer, the International CRC

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Subtyping Consortium developed the consensus molecular subtypes (CMS) classification with four subtypes: CMS1 (MSI immune), CMS2 (canonical), CMS3 (metabolic) and CMS4 (mesenchymal).

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Previously, the gene expression-based subtyping was widely accepted as a tool for disease stratification. However, inconsistencies, probably related to differences in used platforms, sample

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preparation methods and data processing and algorithms, hampered its translational and clinical utility. Next to characterizing the key biological features of the four main subtypes, the CMS subtypes

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also correlate with patient outcome [80]. Interestingly, an association between tumor sidedness and CMS subtypes 1 and 2 was observed. CMS1 tumors were more frequently diagnosed in right-sided lesions [80, 81]. This subtype of CRC is characterized by MSI, CIMP-high, hypermutability, BRAF

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mutations and immune infiltration and activation. In addition, the CMS1 population was associated with worse survival rates after relapse [80]. Conversely CMS2 tumors were mainly observed in leftsided CRC and are characterized by somatic copy number alterations and WNT and MYC activation

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[80, 81]. This subtype is associated with a superior survival rate after relapse and a larger proportion of long-term survivors [80]. Recently, Lenz et al. (2017) presented a CMS analysis of the data from the CALGB/SWOG 80405 study. CMS was defined for 392 of 431 tumors using a custom CRC Nanostring panel. Distribution of CMS subgroups was as follows: CMS1: 14%, CMS2: 47%, CMS3: 2%, CMS4: 29%, non-consensus: 8%. In right-sided tumors a higher incidence of CMS1 was reported compared to left-sided tumors (37%

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vs 9%), while CMS2 was more prevalent in left-sided tumors compared to right-sided tumors (48% vs 23%). CMS2 subtype had the best OS (39.7 months) while CMS1 had the worst OS (17 months). Patients with CMS1 who received a combination with bevacizumab had significantly longer OS than those who received cetuximab, while patients with CMS2 who received bevacizumab tended to have shorter OS than those who received cetuximab [82]. In a similar way, Stintzing et al. (2017) recently presented a CMS analysis of the data from the FIRE-3 study, using ALMAC’s Xcel tissue array. In this population, CMS frequencies were: CMS1: 10.4%, CMS2: 36.6%, CMS3: 11.7%, CMS4: 29.1%, non-

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consensus: 12.2%, which is in striking accordance with the frequencies reported from the CALGB/SWOG 80405 data. Again, CMS1 was the prevalent subtype in right-sided tumors (59%). CMS2 had the best OS followed by CMS4, CMS3 and CMS1 which was in agreement with the

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CALGB/SWOG 80405 results. Survival gain in terms of OS in the cetuximab arm was present in CMS4,

CMS2 and CMS1 and no CMS subtype was favored by the bevacizumab combination, which was in contrast to the analysis mentioned above [83]. Summarizing the CMS reports from both trials, we

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conclude that there is high consistency in the CMS analysis results within the two trials, except for the difference in OS between both treatment arms in CMS1. Although the CMS subtypes were not

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designed to be a predictive tool, now it seems that the subtypes might be useful as a predictive tool.

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However, these data are still immature and at the moment we do not see clinical applicability of

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these results. Future trials should certainly consider to incorporate CMS subtypes in their design.

4.5 Mutations

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It is known that genetic alterations are more frequent in right-sided tumors [62, 84]. Initially, it was attributed to the higher frequency of MSI tumors. Interestingly, it has been reported that the number of mutations was still higher in right-sided carcinomas, even when comparing only microsatellite

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stable (MSS) tumors or excluding MSI-high tumors [9, 84]. When considering oncogenes, a higher mutation rate was observed in right-sided CRC, indicating that this is potentially an important feature

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of right-sided tumors beyond the MSI/hypermutated status. This was confirmed by the observation that important signaling pathways such as MAPK, ErbB, TGF-β and insulin signaling pathways were more frequently mutated in right-sided than in left-sided carcinomas [9].

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4.5.1 KRAS KRAS mutations were more frequently observed in right-sided tumors than left-sided tumors [23, 41, 57, 58, 84-87]. In addition, when comparing left-sided tumors to rectal tumors, rectal tumors more often harbored KRAS mutations [88]. Caecal cancers exhibited the highest frequency of KRAS mutations [60]. In addition, certain studies concluded that KRAS mutations showed a tendency to occur more frequently at the right side, but failed to produce significant results, [89, 90] whereas

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other reports concluded that KRAS mutations occurred at similar frequencies throughout the colorectum [91]. 4.5.2 NRAS NRAS mutations were more frequently observed in left-sided CRC compared to right-sided CRC [84, 92, 93] and more frequently in rectal cancer than in colon cancer [90]. Thus, NRAS mutations show a gradual increase in frequency moving from right to left colon and even more to the rectum. However, in some studies no significant differences in mutation rate between left- and right-sided

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CRC were detected, only a numerical trend towards higher frequency of NRAS mutations [94] or even no difference was observed [85].

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4.5.3 BRAF BRAF mutations were significantly more frequently reported in right-sided tumors compared to leftsided tumors [9, 23, 41, 57, 58, 85, 86, 89, 91, 95-97]. The frequency of BRAF mutations gradually increased from rectum to ascending colon [60, 91]. In contrast, in some other studies, no significant

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differences in the frequency of BRAF mutations were observed between left-sided, right-sided and

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rectal cancers [87, 88, 90, 94, 98]. In addition, it has also been shown that patients with BRAF mutant (mt) CRC have a significantly worse prognosis than BRAF wt tumors. Since BRAF mt tumors are more

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frequent in right-sided tumors, it was previously hypothesized that BRAF mutations were responsible

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for the difference in prognosis between left- and right-sided tumors. However, it has been proven that after correction for this variable, patients with right-sided tumors still have a significantly worse

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prognosis than those with left-sided CRC [15, 29, 38].

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4.5.4 PIK3CA Since PIK3CA mutations in exon 20 are associated with resistance to anti-EGFR therapy, it is of interest to study its association with tumor sidedness [99]. Several studies reported significantly more PIK3CA mutations in right-sided carcinomas [9, 41, 58, 84, 100, 101]. In addition, some studies

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showed that there was a non-significant trend towards more PIK3CA mutations in right-sided CRC [86, 89, 90]. It has been observed that the prevalence of PIK3CA mutations gradually increased from rectal to caecal cancers [84, 102, 103]. Furthermore, there was even a higher frequency of PIK3CA

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mutations in non-hypermutant MSS right-sided colorectal carcinomas [9]. This indicates that the difference in frequency of PIK3CA mutations is not only due to the higher frequency of MSI in rightsided CRC. In contrast, no difference in PIK3CA mutation rate was observed in certain studies [85, 87, 94, 98].

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4.5.5 TP53 Different studies showed that left-sided tumors have significantly more TP53 mutations [58, 84, 87, 104] than right-sided tumors, while other studies showed numerically higher frequencies, but failed to reach significance [90, 94, 96].

4.6 Gene expression

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4.6.1 VEGF-1expression Bendardaf et al. (2008) have shown that VEGF-1 was mostly expressed in tumors located in the left colon and rectum compared to tumors in the right colon [105]. In contrast, another study, reported no significant difference in VEGF expression according to tumor location, when comparing the right-

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and left-sided colon, rectosigmoid and rectum [19].

4.6.2 ERCC1 expression The Excision Repair Cross-Complementation Group 1 (ERCC1) gene codes for a protein, which is involved in DNA repair. Consequently, reduced or absent ERCC1 protein expression leads to impaired

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DNA repair and cells that are more sensitive to DNA damaging agents and accumulation of DNA

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damage. Right-sided tumors expressed significantly higher levels of ERCC1 mRNA according to

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Loupakis et al. (2015) [15]. In contrast, when comparing four locations (right- and left-sided colon, rectosigmoid and rectum), the highest level of ERCC1 expression was noted in the rectosigmoid, but

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when right- and left-sided CRC were compared, no difference in expression of ERCC1 was observed [19].

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4.6.3 PTEN expression Phosphatase and tensin homolog (PTEN) is a protein that functions as a tumor suppressor. PTEN

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inhibits activity in the PIK3CA branch of the EGFR signaling pathway. Therefore loss of PTEN function is associated with poor response to anti-EGFR therapy [106]. PTEN mRNA expression differed

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significantly between left- and right-sided CRC. When rectal cancers were separated from left-sided colon cancers, PTEN mRNA levels increased progressively from rectum to right-sided colon [107]. Similarly, PTEN loss was reported in 27.6% of mCRC patients with right-sided tumors compared to 53% in patients with left-sided tumors (p=0.01) [45]. However, other studies showed no significant

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difference in PTEN expression [41, 58]. 4.6.4 Epiregulin and amphiregulin expression Epiregulin and amphiregulin can act as a ligand of EGFR. Both epiregulin and amphiregulin expression were significantly higher in patients with primary tumor location in the left part of the colon compared to the right part [9, 41, 74, 108, 109].

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5. Discussion and conclusion In this review, a comprehensive overview of the latest trials studying the predictive value of primary tumor location in mCRC was provided. In addition, biomarkers that might be associated with these different therapeutic responses were discussed. First, we discussed several trials that studied the predictive value of primary tumor location. The reviewed data show evidence that in left-sided CRC the addition of anti-EGFR therapy to chemotherapy or BSC resulted in better survival outcomes compared to chemotherapy, BSC alone or

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the addition of anti-VEGF therapy to chemotherapy in first- and later-line treatment [25, 30, 31, 33,

38-41, 44]. However, for right-sided CRC the results are contradicting and the data did not allow drawing definitive conclusions about the efficacy of anti-VEGF and anti-EGFR treatment due to

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limited sample sizes.

Given the lack of randomized data, the predictive role of primary tumor location has not yet been included in the latest guidelines. Solely, the National Comprehensive Cancer Network guidelines for

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CRC recommend that only patients whose primary tumor originated on the left side of the colon (splenic flexure to rectum) should be offered cetuximab or panitumumab (anti-EGFR therapy) in first-

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line treatment of mCRC [110]. The ESMO guidelines for the management of patients with mCRC

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published in 2016 and ASCO guidelines about molecular biomarkers for the evaluation of CRC, did

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not yet change according to tumor location [111, 112].

However, based on the presented results and our experience in clinic, we are convinced that patients with right- and left-sided tumors should be treated differently as described by Arnold et al. (2017)

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[47]. We suggest to treat patients with left-sided wildtype disease with a chemotherapy doublet and anti-EGFR therapy when the treatment goal is cytoreduction, while the preferred therapy option is a

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chemotherapy doublet or triplet and bevacizumab in patients with left-sided mutant disease. In case treatment goal is disease stabilization, patients with left-sided wildtype CRC should be treated with a

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chemotherapy doublet and anti-EGFR therapy. However a chemotherapy doublet and bevacizumab is also an option. For patients with left-sided mutant disease, a chemotherapy doublet plus bevacizumab is the preferred option for disease stabilization. In patients with right-sided CRC when the treatment goal is cytoreduction, the preferred treatment

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option is a chemotherapy doublet plus anti-EGFR therapy or bevacizumab, while patients with mutant disease (including BRAF) should receive FOLFOXIRI and anti-EGFR therapy or bevacizumab. For patients with right-sided disease for whom the treatment goal is disease stabilization, the preferred treatment option is a chemotherapy doublet plus bevacizumab for wildtype tumors, RAS mutant tumors should be treated with a chemotherapy doublet or triplet and bevacizumab, and BRAF mutant tumors should receive a chemotherapy triplet and bevacizumab. These suggestions can of course be modified based on performance status or a comorbidity. 13

Secondly, we made an overview of the biomarkers that are differently expressed along the colon which might contribute to the differences in clinical presentation and response to therapy in left- and right-sided CRC. Certain differences in gut content, genomic instability, mutational status and gene expression are the most important factors that vary along the course of the colon. How these biomarkers are associated to prognostic and predictive differences is in many cases unclear and remains to be elucidated. A note of caution is due since all data are based on trials with certain limitations. A first point is the

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lack of randomized trials. Furthermore, as in all unplanned retrospective studies, there is a potential for bias from unbalanced population selection, leading to imbalances in certain baseline

characteristics and small numbers of patients in some subgroups. These imbalances may have

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influenced the outcomes and therefore prospective trials are needed to confirm the data reported in the retrospective trials. Secondly, because of the small sample sizes in some subgroups, caution must be applied. Especially the right-sided tumor cohorts were relatively small, resulting in low power of

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the studies. Lastly, as described in the introduction, the demarcation line for the definition of leftand right-sided CRC differed in several studies and in some studies the rectum was considered as a

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third separate group. Therefore it is important to bear in mind the possible bias caused by the

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difference in definition of left- and right-sided tumors. Also, in practice it is in certain cases difficult to

M

identify the location of the primary tumor, especially when there is no excision of the tumor. Furthermore, tumors originating in the distal third of the transverse colon were defined as rightsided tumors in most studies, even though they are in fact left-sided tumors, based on embryology.

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This might affect the results. However, it needs to be clearly stated that dividing the colon in the left and right part is a simplified dichotomous model which facilitates analysis. The colorectal continuum

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model that is based on the observation that the varying features gradually increase or decrease from rectum to ascending colon might be a more realistic model [60, 113].

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Despite these limitations, the preponderance of available evidence suggests that primary tumor location impacts responsiveness to therapies in mCRC. However, the complex molecular mechanisms causing this difference in response still remain unclear. Future clinical trials in CRC will need to be prospectively stratified using sidedness as a variable, taking into account the specific location of the

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primary tumor. Furthermore, the role of (other) potential biomarkers needs to be clarified in order to allow the identification of specific subgroups responding to certain therapies and in order to determine optimal treatment strategy. Treatment algorithms should be based on the underlying mechanisms that cause the different responses to therapy. Only by identifying these underlying mechanisms, patients can be provided with the best possible personalized therapy.

14

Disclosure All authors have made substantial contributions to the manuscript and they all have approved the final article. Conflicts of interest statement: nothing to be declared.

Acknowledgement

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Funding: This work was supported by grants from National Cancer Plan (grant: NKP 29_38) and FWO

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(G0B4414N).

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References

8. 9.

10.

11.

IP T

CC E

12.

SC R

7.

U

6.

N

5.

A

4.

M

3.

ED

2.

Ferlay, J., I. Soerjomataram, R. Dikshit, S. Eser, C. Mathers, M. Rebelo, et al., Cancer incidence and mortality worldwide: sources, methods and major patterns in GLOBOCAN 2012. Int J Cancer, 2015. 136(5): p. E359-86. Brungs, D., M. Aghmesheh, P. de Souza, W. Ng, W. Chua, M. Carolan, et al., Sidedness is prognostic in locoregional colon cancer: an analysis of 9509 Australian patients. BMC cancer, 2017. 17(1): p. 251. Benedix, F., R. Kube, F. Meyer, U. Schmidt, I. Gastinger, H. Lippert, et al., Comparison of 17,641 patients with right- and left-sided colon cancer: differences in epidemiology, perioperative course, histology, and survival. Dis Colon Rectum, 2010. 53(1): p. 57-64. Gonzalez, E.C., R.G. Roetzheim, J.M. Ferrante, and R. Campbell, Predictors of proximal vs. distal colorectal cancers. Dis Colon Rectum, 2001. 44(2): p. 251-8. Yang, J., X.L. Du, S.T. Li, B.Y. Wang, Y.Y. Wu, Z.L. Chen, et al., Characteristics of Differently Located Colorectal Cancers Support Proximal and Distal Classification: A Population-Based Study of 57,847 Patients. PloS one, 2016. 11(12): p. e0167540. Mik, M., M. Berut, L. Dziki, R. Trzcinski, and A. Dziki, Right- and left-sided colon cancer clinical and pathological differences of the disease entity in one organ. Arch Med Sci, 2017. 13(1): p. 157-162. Saltzstein, S.L. and C.A. Behling, Age and time as factors in the left-to-right shift of the subsite of colorectal adenocarcinoma: a study of 213,383 cases from the California Cancer Registry. J Clin Gastroenterol, 2007. 41(2): p. 173-7. Riihimaki, M., A. Hemminki, J. Sundquist, and K. Hemminki, Patterns of metastasis in colon and rectal cancer. Sci Rep, 2016. 6: p. 29765. Missiaglia, E., B. Jacobs, G. D'Ario, A.F. Di Narzo, C. Soneson, E. Budinska, et al., Distal and proximal colon cancers differ in terms of molecular, pathological, and clinical features. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2014. 25(10): p. 1995-2001. Sideris, M., K. Adams, J. Moorhead, S. Diaz-Cano, I. Bjarnason, and S. Papagrigoriadis, BRAF V600E mutation in colorectal cancer is associated with right-sided tumours and iron deficiency anaemia. Anticancer Res, 2015. 35(4): p. 2345-50. Edna, T.H., V. Karlsen, E. Jullumstro, and S. Lydersen, Prevalence of anaemia at diagnosis of colorectal cancer: assessment of associated risk factors. Hepatogastroenterology, 2012. 59(115): p. 713-6. Keeler, B.D., A. Mishra, C.L. Stavrou, S. Beeby, J.A. Simpson, and A.G. Acheson, A cohort investigation of anaemia, treatment and the use of allogeneic blood transfusion in colorectal cancer surgery. Ann Med Surg (Lond), 2016. 6: p. 6-11. Ghazi, S., U. Lindforss, G. Lindberg, E. Berg, A. Lindblom, N. Papadogiannakis, et al., Analysis of colorectal cancer morphology in relation to sex, age, location, and family history. J Gastroenterol, 2012. 47(6): p. 619-34. Hemminki, K., I. Santi, M. Weires, H. Thomsen, J. Sundquist, and J.L. Bermejo, Tumor location and patient characteristics of colon and rectal adenocarcinomas in relation to survival and TNM classes. BMC cancer, 2010. 10: p. 688. Loupakis, F., D. Yang, L. Yau, S. Feng, C. Cremolini, W. Zhang, et al., Primary tumor location as a prognostic factor in metastatic colorectal cancer. J Natl Cancer Inst, 2015. 107(3). Li, P., Z. Xiao, T.A. Braciak, Q. Ou, G. Chen, and F.S. Oduncu, A relationship to survival is seen by combining the factors of mismatch repair status, tumor location and age of onset in colorectal cancer patients. PloS one, 2017. 12(3): p. e0172799. Russo, A., V. Bazan, B. Iacopetta, D. Kerr, T. Soussi, N. Gebbia, et al., The TP53 colorectal cancer international collaborative study on the prognostic and predictive significance of p53

PT

1.

13.

A

14.

15. 16.

17.

16

25.

26.

27.

28.

29.

IP T

CC E

30.

SC R

24.

U

23.

N

22.

A

21.

M

20.

ED

19.

PT

18.

mutation: influence of tumor site, type of mutation, and adjuvant treatment. J Clin Oncol, 2005. 23(30): p. 7518-28. Jayasekara, H., J.C. Reece, D.D. Buchanan, C. Rosty, S.G. Dashti, D. Ait Ouakrim, et al., Risk factors for metachronous colorectal cancer following a primary colorectal cancer: A prospective cohort study. Int J Cancer, 2016. 139(5): p. 1081-90. Shimamoto, Y., M. Nukatsuka, T. Takechi, and M. Fukushima, Association between mRNA expression of chemotherapy-related genes and clinicopathological features in colorectal cancer: A large-scale population analysis. Int J Mol Med, 2016. 37(2): p. 319-28. Cucino, C., F. Parente, and G. Bianchi Porro, Rightward shift of colorectal cancer in Italy during the past three decades. Scand J Gastroenterol, 2004. 39(8): p. 783-6. Cucino, C., A.M. Buchner, and A. Sonnenberg, Continued rightward shift of colorectal cancer. Dis Colon Rectum, 2002. 45(8): p. 1035-40. Cheng, L., C. Eng, L.Z. Nieman, A.S. Kapadia, and X.L. Du, Trends in colorectal cancer incidence by anatomic site and disease stage in the United States from 1976 to 2005. Am J Clin Oncol, 2011. 34(6): p. 573-80. Lee B, Mendis S, Lee M, et al. Left versus right sided colorectal cancer: Teasing out drivers of disparity in outcomes in metastatic disease. J Clin Oncol 35, 2017 (suppl 4S; abstract 682). Shen, H., J. Yang, Q. Huang, M.J. Jiang, Y.N. Tan, J.F. Fu, et al., Different treatment strategies and molecular features between right-sided and left-sided colon cancers. World J Gastroenterol, 2015. 21(21): p. 6470-8. Venook A, Niedzwiecki D, Innocenti F, et al. Impact of primary tumor location on overall survival and progression-free survival in patients with metastatic colorectal cancer: analysis of CALGB/SWOG 80405 (Alliance). J Clin Oncol. 2016; 34(suppl, abstr 3504). Meguid, R.A., M.B. Slidell, C.L. Wolfgang, D.C. Chang, and N. Ahuja, Is there a difference in survival between right- versus left-sided colon cancers? Ann Surg Oncol, 2008. 15(9): p. 238894. Price, T.J., C. Beeke, S. Ullah, R. Padbury, G. Maddern, D. Roder, et al., Does the primary site of colorectal cancer impact outcomes for patients with metastatic disease? Cancer, 2015. 121(6): p. 830-5. Holch, J.W., I. Ricard, S. Stintzing, D.P. Modest, and V. Heinemann, The relevance of primary tumour location in patients with metastatic colorectal cancer: A meta-analysis of first-line clinical trials. Eur J Cancer, 2017. 70: p. 87-98. Sunakawa, Y., W. Ichikawa, A. Tsuji, T. Denda, Y. Segawa, Y. Negoro, et al., Prognostic Impact of Primary Tumor Location on Clinical Outcomes of Metastatic Colorectal Cancer Treated With Cetuximab Plus Oxaliplatin-Based Chemotherapy: A Subgroup Analysis of the JACCRO CC-05/06 Trials. Clin Colorectal Cancer, 2016. Lu, H.J., J.K. Lin, W.S. Chen, J.K. Jiang, S.H. Yang, Y.T. Lan, et al., Primary tumor location is an important predictive factor for wild-type KRAS metastatic colon cancer treated with cetuximab as front-line bio-therapy. Asia Pac J Clin Oncol, 2016. 12(3): p. 207-15. Tejpar, S., S. Stintzing, F. Ciardiello, J. Tabernero, E. Van Cutsem, F. Beier, et al., Prognostic and Predictive Relevance of Primary Tumor Location in Patients With RAS Wild-Type Metastatic Colorectal Cancer: Retrospective Analyses of the CRYSTAL and FIRE-3 Trials. JAMA Oncol, 2016. Miyamoto, Y., N. Hayashi, Y. Sakamoto, M. Ohuchi, R. Tokunagam, J. Kurashige, et al., Predictors of long-term survival in patients with stage IV colorectal cancer with multi-organ metastases: a single-center retrospective analysis. Int J Clin Oncol, 2015. 20(6): p. 1140-6. Wang, F., L. Bai, T.S. Liu, Y.Y. Yu, M.M. He, K.Y. Liu, et al., Right-sided colon cancer and leftsided colorectal cancers respond differently to cetuximab. Chin J Cancer, 2015. 34(9): p. 38493. Petrelli, F., G. Tomasello, K. Borgonovo, M. Ghidini, L. Turati, P. Dallera, et al., Prognostic Survival Associated With Left-Sided vs Right-Sided Colon Cancer: A Systematic Review and Meta-analysis. JAMA Oncol, 2016.

A

31.

32.

33.

34.

17

42.

43.

44.

45.

IP T

CC E

46.

SC R

41.

U

40.

N

39.

A

38.

M

37.

ED

36.

Yahagi, M., K. Okabayashi, H. Hasegawa, M. Tsuruta, and Y. Kitagawa, The Worse Prognosis of Right-Sided Compared with Left-Sided Colon Cancers: a Systematic Review and Meta-analysis. J Gastrointest Surg, 2016. 20(3): p. 648-55. Oldenhuis, C.N., S.F. Oosting, J.A. Gietema, and E.G. de Vries, Prognostic versus predictive value of biomarkers in oncology. Eur J Cancer, 2008. 44(7): p. 946-53. Nalejska, E., E. Maczynska, and M.A. Lewandowska, Prognostic and predictive biomarkers: tools in personalized oncology. Mol Diagn Ther, 2014. 18(3): p. 273-84. Boeckx, N., R. Koukakis, K. Op de Beeck, C. Rolfo, G. Van Camp, S. Siena, et al., Primary tumor sidedness has an impact on prognosis and treatment outcome in metastatic colorectal cancer: results from two randomized first-line panitumumab studies. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2017. Qin S, Xu J, Wang L, et al. Impact of primary tumor location (TL) on outcomes of first-line (1L) FOLFOX-4 (F) ± cetuximab (cet) in patients (pts) with RAS wild-type (wt) metastatic colorectal cancer (mCRC) in the phase 3 TAILOR trial. J Clin Oncol 35, 2017 (suppl 4S; abstract 683). Boeckx, N., A. Toler, K. Op de Beeck, G. Kafatos, V. Deschoolmeester, C. Rolfo, et al., Primary tumor sidedness impacts on prognosis and treatment outcome: results from three randomized studies of panitumumab plus chemotherapy versus chemotherapy or chemotherapy plus bevacizumab in 1st and 2nd line RAS/BRAF WT mCRC. Annals of Oncology (2016) 27 (6): 15-42. 10.1093/annonc/mdw363 (abstract 89P). Brule, S.Y., D.J. Jonker, C.S. Karapetis, C.J. O'Callaghan, M.J. Moore, R. Wong, et al., Location of colon cancer (right-sided versus left-sided) as a prognostic factor and a predictor of benefit from cetuximab in NCIC CO.17. Eur J Cancer, 2015. 51(11): p. 1405-14. He, W.Z., F.X. Liao, C. Jiang, P.F. Kong, C.X. Yin, Q. Yang, et al., Primary Tumor Location as a Predictive Factor for First-line Bevacizumab Effectiveness in Metastatic Colorectal Cancer Patients. J Cancer, 2017. 8(3): p. 388-394. Portnoy DC, Obermannova R, Bodoky G, et al. Exploratory analysis of left- versus right-sided colorectal carcinoma in RAISE: A randomized, double-blind, phase 3 trial of ramucirumab (RAM) + FOLFIRI versus placebo (PBO) + FOLFIRI. J Clin Oncol 35, 2017 (suppl 4S; abstract 668). Sagawa T, Hamaguchi K, Sakurada A, et al. Primary tumor location as a prognostic and predictive factor in metastatic colorectal cancer (mCRC) treated with chemotherapy plus cetuximab: A retrospective analysis. J Clin Oncol 35, 2017 (suppl 4S; abstract 711). Price, T.J., L. Buizen, J.E. Hardingham, C.K. Lee, A.R. Townsend, M. Bruhn, et al., Molecular subgroups from the AGITG MAX trial; right or left primary site of colorectal cancer and outcomes for metastatic colorectal cancer (mCRC). Annals of Oncology, Volume 25, Issue suppl_4, 1 September 2014, Pages iv173, https://doi.org/10.1093/annonc/mdu333.14. Boisen, M.K., J.S. Johansen, C. Dehlendorff, J.S. Larsen, K. Osterlind, J. Hansen, et al., Primary tumor location and bevacizumab effectiveness in patients with metastatic colorectal cancer. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2013. 24(10): p. 2554-9. Arnold, D., B. Lueza, J.Y. Douillard, M. Peeters, H.J. Lenz, A. Venook, et al., Prognostic and predictive value of primary tumour side in patients with RAS wild-type metastatic colorectal cancer treated with chemotherapy and EGFR directed antibodies in six randomized trials. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2017. 28(8): p. 1713-1729. Gagniere, J., J. Raisch, J. Veziant, N. Barnich, R. Bonnet, E. Buc, et al., Gut microbiota imbalance and colorectal cancer. World J Gastroenterol, 2016. 22(2): p. 501-18. Mima, K., Y. Cao, A.T. Chan, Z.R. Qian, J.A. Nowak, Y. Masugi, et al., Fusobacterium nucleatum in Colorectal Carcinoma Tissue According to Tumor Location. Clin Transl Gastroenterol, 2016. 7(11): p. e200.

PT

35.

A

47.

48. 49.

18

57.

58.

59.

60.

IP T

CC E

61.

SC R

56.

U

55.

N

54.

A

53.

M

52.

ED

51.

Yu, J., Y. Chen, X. Fu, X. Zhou, Y. Peng, L. Shi, et al., Invasive Fusobacterium nucleatum may play a role in the carcinogenesis of proximal colon cancer through the serrated neoplasia pathway. Int J Cancer, 2016. 139(6): p. 1318-26. Hold, G.L. and W.S. Garrett, Gut microbiota. Microbiota organization--a key to understanding CRC development. Nat Rev Gastroenterol Hepatol, 2015. 12(3): p. 128-9. Dejea, C.M., E.C. Wick, E.M. Hechenbleikner, J.R. White, J.L. Mark Welch, B.J. Rossetti, et al., Microbiota organization is a distinct feature of proximal colorectal cancers. Proc Natl Acad Sci U S A, 2014. 111(51): p. 18321-6. Johnson, C.H., C.M. Dejea, D. Edler, L.T. Hoang, A.F. Santidrian, B.H. Felding, et al., Metabolism links bacterial biofilms and colon carcinogenesis. Cell Metab, 2015. 21(6): p. 8917. Hawkins, N., M. Norrie, K. Cheong, E. Mokany, S.L. Ku, A. Meagher, et al., CpG island methylation in sporadic colorectal cancers and its relationship to microsatellite instability. Gastroenterology, 2002. 122(5): p. 1376-87. Simons, C.C., L.A. Hughes, K.M. Smits, C.A. Khalid-de Bakker, A.P. de Bruine, B. Carvalho, et al., A novel classification of colorectal tumors based on microsatellite instability, the CpG island methylator phenotype and chromosomal instability: implications for prognosis. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2013. 24(8): p. 2048-56. Sanz-Pamplona, R., D. Cordero, A. Berenguer, F. Lejbkowicz, H. Rennert, R. Salazar, et al., Gene expression differences between colon and rectum tumors. Clin Cancer Res, 2011. 17(23): p. 7303-12. Lin, L., G.Y. Chen, C.W. Xu, H.Y. Wang, Y.F. Wu, and M.Y. Fang, Evaluation and identification of factors related to KRAS and BRAF gene mutations in colorectal cancer: A meta-analysis. J Cancer Res Ther, 2016. 12(Supplement): p. C191-C198. Chang, S.C., P.C. Lin, J.K. Lin, C.H. Lin, S.H. Yang, W.Y. Liang, et al., Mutation Spectra of Common Cancer-Associated Genes in Different Phenotypes of Colorectal Carcinoma Without Distant Metastasis. Ann Surg Oncol, 2016. 23(3): p. 849-55. Arriba, M., R. Sanchez, D. Rueda, L. Gomez, J.L. Garcia, Y. Rodriguez, et al., Toward a Molecular Classification of Synchronous Colorectal Cancer: Clinical and Molecular Characterization. Clin Colorectal Cancer, 2017. 16(1): p. 31-37. Yamauchi, M., T. Morikawa, A. Kuchiba, Y. Imamura, Z.R. Qian, R. Nishihara, et al., Assessment of colorectal cancer molecular features along bowel subsites challenges the conception of distinct dichotomy of proximal versus distal colorectum. Gut, 2012. 61(6): p. 847-54. Wang, J.B., D.L. Ma, J.Y. Li, Q.D. Sun, and Y.E. Liu, Association between expression of DNA mismatch repair genes and clinical features and prognosis of patients with radical resection of colon cancer. Genet Mol Res, 2016. 15(3). Cancer Genome Atlas, N., Comprehensive molecular characterization of human colon and rectal cancer. Nature, 2012. 487(7407): p. 330-7. Innocenti, F., F.-S. Ou, T. Zemla, D. Niedzwiecki, X. Qu, R. Tam, et al., Somatic DNA mutations, MSI status, mutational load (ML): Association with overall survival (OS) in patients (pts) with metastatic colorectal cancer (mCRC) of CALGB/SWOG 80405 (Alliance). DOI: 10.1200/JCO.2017.35.15_suppl.3504 Journal of Clinical Oncology 35, no. 15_suppl (May 2017) 3504-3504. Perea, J., J.M. Cano, D. Rueda, J.L. Garcia, L. Inglada, I. Osorio, et al., Classifying early-onset colorectal cancer according to tumor location: new potential subcategories to explore. Am J Cancer Res, 2015. 5(7): p. 2308-13. Toyota, M., N. Ahuja, M. Ohe-Toyota, J.G. Herman, S.B. Baylin, and J.P. Issa, CpG island methylator phenotype in colorectal cancer. Proc Natl Acad Sci U S A, 1999. 96(15): p. 8681-6. Zhang, X., H. Shimodaira, H. Soeda, K. Komine, H. Takahashi, K. Ouchi, et al., CpG island methylator phenotype is associated with the efficacy of sequential oxaliplatin- and irinotecan-

PT

50.

62.

A

63.

64.

65. 66.

19

74.

75.

76.

77.

IP T

CC E

78.

SC R

73.

U

72.

N

71.

A

70.

M

69.

ED

68.

PT

67.

based chemotherapy and EGFR-related gene mutation in Japanese patients with metastatic colorectal cancer. Int J Clin Oncol, 2016. 21(6): p. 1091-1101. Weisenberger, D.J., K.D. Siegmund, M. Campan, J. Young, T.I. Long, M.A. Faasse, et al., CpG island methylator phenotype underlies sporadic microsatellite instability and is tightly associated with BRAF mutation in colorectal cancer. Nature genetics, 2006. 38(7): p. 787-93. Slattery, M.L., K. Curtin, R.K. Wolff, K.M. Boucher, C. Sweeney, S. Edwards, et al., A comparison of colon and rectal somatic DNA alterations. Dis Colon Rectum, 2009. 52(7): p. 1304-11. Toyota, M., M. Ohe-Toyota, N. Ahuja, and J.P. Issa, Distinct genetic profiles in colorectal tumors with or without the CpG island methylator phenotype. Proc Natl Acad Sci U S A, 2000. 97(2): p. 710-5. English, D.R., J.P. Young, J.A. Simpson, M.A. Jenkins, M.C. Southey, M.D. Walsh, et al., Ethnicity and risk for colorectal cancers showing somatic BRAF V600E mutation or CpG island methylator phenotype. Cancer Epidemiol Biomarkers Prev, 2008. 17(7): p. 1774-80. Nosho, K., N. Irahara, K. Shima, S. Kure, G.J. Kirkner, E.S. Schernhammer, et al., Comprehensive biostatistical analysis of CpG island methylator phenotype in colorectal cancer using a large population-based sample. PloS one, 2008. 3(11): p. e3698. Shen, L., P.J. Catalano, A.B. Benson, 3rd, P. O'Dwyer, S.R. Hamilton, and J.P. Issa, Association between DNA methylation and shortened survival in patients with advanced colorectal cancer treated with 5-fluorouracil based chemotherapy. Clin Cancer Res, 2007. 13(20): p. 6093-8. Samowitz, W.S., H. Albertsen, J. Herrick, T.R. Levin, C. Sweeney, M.A. Murtaugh, et al., Evaluation of a large, population-based sample supports a CpG island methylator phenotype in colon cancer. Gastroenterology, 2005. 129(3): p. 837-45. Lee, M.S., E.J. McGuffey, J.S. Morris, G. Manyam, V. Baladandayuthapani, W. Wei, et al., Association of CpG island methylator phenotype and EREG/AREG methylation and expression in colorectal cancer. Br J Cancer, 2016. 114(12): p. 1352-61. Zong, L., M. Abe, J. Ji, W.G. Zhu, and D. Yu, Tracking the Correlation Between CpG Island Methylator Phenotype and Other Molecular Features and Clinicopathological Features in Human Colorectal Cancers: A Systematic Review and Meta-Analysis. Clin Transl Gastroenterol, 2016. 7: p. e151. Jia, M., L. Jansen, V. Walter, K. Tagscherer, W. Roth, E. Herpel, et al., No association of CpG island methylator phenotype and colorectal cancer survival: population-based study. Br J Cancer, 2016. 115(11): p. 1359-1366. Curtin, K., M.L. Slattery, and W.S. Samowitz, CpG island methylation in colorectal cancer: past, present and future. Patholog Res Int, 2011. 2011: p. 902674. Tang, J.T., Z.H. Wang, and J.Y. Fang, Assessing the potential value of long interspersed element-1 hypomethylation in colorectal cancer: evidence from retrospective studies. Onco Targets Ther, 2015. 8: p. 3265-76. Mima, K., J.A. Nowak, Z.R. Qian, Y. Cao, M. Song, Y. Masugi, et al., Tumor LINE-1 methylation level and colorectal cancer location in relation to patient survival. Oncotarget, 2016. 7(34): p. 55098-55109. Guinney, J., R. Dienstmann, X. Wang, A. de Reynies, A. Schlicker, C. Soneson, et al., The consensus molecular subtypes of colorectal cancer. Nat Med, 2015. 21(11): p. 1350-6. Kwon, Y., M. Park, M. Jang, S. Yun, W.K. Kim, S. Kim, et al., Prognosis of stage III colorectal carcinomas with FOLFOX adjuvant chemotherapy can be predicted by molecular subtype. Oncotarget, 2017. Lenz HJ, O.F., Venook AP at al Impact of consensus molecular subtyping (CMS) on overall survival (OS) and progression free survival (PFS) in patients (pts) with metastatic colorectal cancer (mCRC): Analysis of CALGB/SWOG 80405 (Alliance). ASCO 2017 Abstract 3511. Stintzing S, W.P., Lenz HJ at al Consensus Molecular Subgroups (CMS) of Colorectal Cancer (CRC) and 1st Line Efficacy of FOLFIRI Plus Cetuximab or Bevacizumab: Analysis of the FIRE-3 (AIO KRK 0306) Study ASCO 2017 abstract 3510.

79.

A

80. 81.

82.

83.

20

91.

92. 93.

94.

95.

IP T

CC E

96.

SC R

90.

U

89.

N

88.

A

87.

M

86.

ED

85.

Lee, D.W., S.W. Han, Y. Cha, J.M. Bae, H.P. Kim, J. Lyu, et al., Association between mutations of critical pathway genes and survival outcomes according to the tumor location in colorectal cancer. Cancer, 2017. Inagaki D, Shiozawa M, Satoyoshi T, et al. Relationship between tumor location and oncogenes mutations (RAS, BRAF, and PIK3CA) in colorectal cancer. J Clin Oncol 35, 2017 (suppl 4S; abstract 580). Zhang, J., J. Zheng, Y. Yang, J. Lu, J. Gao, T. Lu, et al., Molecular spectrum of KRAS, NRAS, BRAF and PIK3CA mutations in Chinese colorectal cancer patients: analysis of 1,110 cases. Sci Rep, 2015. 5: p. 18678. Takahashi, Y., T. Sugai, W. Habano, K. Ishida, M. Eizuka, K. Otsuka, et al., Molecular differences in the microsatellite stable phenotype between left-sided and right-sided colorectal cancer. Int J Cancer, 2016. 139(11): p. 2493-501. Salem ME, Yin J, Renfro LA, et al. Rectal versus left-sided colon cancers: Clinicopathological differences observed in a pooled analysis of 4,182 patients enrolled to 8 clinical trials from the ARCAD database. J Clin Oncol 35, 2017 (suppl 4S; abstract 675). Jensen CE, Loaiza-Bonilla A, Villanueva JY, et al. Differences in mutation rates between rightand left-sided colorectal adenocarcinoma. J Clin Oncol 35, 2017 (suppl 4S; abstract 622). Jauhri, M., A. Bhatnagar, S. Gupta, M. Bp, S. Minhas, Y. Shokeen, et al., Prevalence and coexistence of KRAS, BRAF, PIK3CA, NRAS, TP53, and APC mutations in Indian colorectal cancer patients: Next-generation sequencing-based cohort study. Tumour Biol, 2017. 39(2): p. 1010428317692265. Maus, M.K., D.L. Hanna, C.L. Stephens, S.H. Astrow, D. Yang, P.P. Grimminger, et al., Distinct gene expression profiles of proximal and distal colorectal cancer: implications for cytotoxic and targeted therapy. Pharmacogenomics J, 2015. 15(4): p. 354-62. Takane, K., K. Akagi, M. Fukuyo, K. Yagi, T. Takayama, and A. Kaneda, DNA methylation epigenotype and clinical features of NRAS-mutation(+) colorectal cancer. Cancer Med, 2017. Cercek, A., M.I. Braghiroli, J.F. Chou, J.F. Hechtman, N.E. Kemeny, L. Saltz, et al., Clinical features and outcomes of patients with colorectal cancers harboring NRAS mutations. Clin Cancer Res, 2017. Al-Shamsi, H.O., J. Jones, Y. Fahmawi, I. Dahbour, A. Tabash, R. Abdel-Wahab, et al., Molecular spectrum of KRAS, NRAS, BRAF, PIK3CA, TP53, and APC somatic gene mutations in Arab patients with colorectal cancer: determination of frequency and distribution pattern. J Gastrointest Oncol, 2016. 7(6): p. 882-902. Loupakis, F., R. Moretto, G. Aprile, M. Muntoni, C. Cremolini, D. Iacono, et al., Clinicopathological nomogram for predicting BRAF mutational status of metastatic colorectal cancer. Br J Cancer, 2016. 114(1): p. 30-6. Mouradov, D., E. Domingo, P. Gibbs, R.N. Jorissen, S. Li, P.Y. Soo, et al., Survival in stage II/III colorectal cancer is independently predicted by chromosomal and microsatellite instability, but not by specific driver mutations. Am J Gastroenterol, 2013. 108(11): p. 1785-93. Kawazoe, A., K. Shitara, S. Fukuoka, Y. Kuboki, H. Bando, W. Okamoto, et al., A retrospective observational study of clinicopathological features of KRAS, NRAS, BRAF and PIK3CA mutations in Japanese patients with metastatic colorectal cancer. BMC cancer, 2015. 15: p. 258. Bisht, S., F. Ahmad, S. Sawaimoon, S. Bhatia, and B.R. Das, Molecular spectrum of KRAS, BRAF, and PIK3CA gene mutation: determination of frequency, distribution pattern in Indian colorectal carcinoma. Med Oncol, 2014. 31(9): p. 124. Mao, C., Z.Y. Yang, X.F. Hu, Q. Chen, and J.L. Tang, PIK3CA exon 20 mutations as a potential biomarker for resistance to anti-EGFR monoclonal antibodies in KRAS wild-type metastatic colorectal cancer: a systematic review and meta-analysis. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2012. 23(6): p. 1518-25.

PT

84.

A

97.

98.

99.

21

102.

103.

104.

105.

109.

A

M

CC E

110. 111.

ED

108.

PT

107.

N

U

106.

IP T

101.

Phipps, A.I., D.J. Ahnen, I. Cheng, P.A. Newcomb, A.K. Win, and T. Burnett, PIK3CA Somatic Mutation Status in Relation to Patient and Tumor Factors in Racial/Ethnic Minorities with Colorectal Cancer. Cancer Epidemiol Biomarkers Prev, 2015. 24(7): p. 1046-51. Shen, Y., J. Wang, X. Han, H. Yang, S. Wang, D. Lin, et al., Effectors of epidermal growth factor receptor pathway: the genetic profiling ofKRAS, BRAF, PIK3CA, NRAS mutations in colorectal cancer characteristics and personalized medicine. PloS one, 2013. 8(12): p. e81628. Ogino, S., P. Lochhead, E. Giovannucci, J.A. Meyerhardt, C.S. Fuchs, and A.T. Chan, Discovery of colorectal cancer PIK3CA mutation as potential predictive biomarker: power and promise of molecular pathological epidemiology. Oncogene, 2014. 33(23): p. 2949-55. Rosty, C., J.P. Young, M.D. Walsh, M. Clendenning, K. Sanderson, R.J. Walters, et al., PIK3CA activating mutation in colorectal carcinoma: associations with molecular features and survival. PloS one, 2013. 8(6): p. e65479. Soong, R., B. Powell, H. Elsaleh, G. Gnanasampanthan, D.R. Smith, H.S. Goh, et al., Prognostic significance of TP53 gene mutation in 995 cases of colorectal carcinoma. Influence of tumour site, stage, adjuvant chemotherapy and type of mutation. Eur J Cancer, 2000. 36(16): p. 205360. Bendardaf, R., A. Buhmeida, M. Hilska, M. Laato, S. Syrjanen, K. Syrjanen, et al., VEGF-1 expression in colorectal cancer is associated with disease localization, stage, and long-term disease-specific survival. Anticancer Res, 2008. 28(6B): p. 3865-70. Therkildsen, C., T.K. Bergmann, T. Henrichsen-Schnack, S. Ladelund, and M. Nilbert, The predictive value of KRAS, NRAS, BRAF, PIK3CA and PTEN for anti-EGFR treatment in metastatic colorectal cancer: A systematic review and meta-analysis. Acta Oncol, 2014. 53(7): p. 852-64. Kuramochi, H., A. Nakamura, G. Nakajima, Y. Kaneko, T. Araida, M. Yamamoto, et al., PTEN mRNA expression is less pronounced in left- than right-sided colon cancer: a retrospective observational study. BMC cancer, 2016. 16: p. 366. Seligmann, J.F., F. Elliott, S.D. Richman, B. Jacobs, G. Hemmings, S. Brown, et al., Combined Epiregulin and Amphiregulin Expression Levels as a Predictive Biomarker for Panitumumab Therapy Benefit or Lack of Benefit in Patients With RAS Wild-Type Advanced Colorectal Cancer. JAMA Oncol, 2016. Adams RA, Fisher D, Farragher S, et al. Use of epiregulin (EREG) and amphiregulin (AREG) gene expression to predict response to cetuximab (cet) in combination with oxaliplatin (Ox) and 5FU in the firstline treatment of advanced colorectal cancer (aCRC). J Clin Oncol 30: 2012 (suppl 30; abstr 32). National Comprehensive Cancer Network, NCCN Guidelines for Colon Cancer, Version 1.2017. Van Cutsem, E., A. Cervantes, R. Adam, A. Sobrero, J.H. Van Krieken, D. Aderka, et al., ESMO consensus guidelines for the management of patients with metastatic colorectal cancer. Annals of oncology : official journal of the European Society for Medical Oncology / ESMO, 2016. 27(8): p. 1386-422. Sepulveda, A.R., S.R. Hamilton, C.J. Allegra, W. Grody, A.M. Cushman-Vokoun, W.K. Funkhouser, et al., Molecular Biomarkers for the Evaluation of Colorectal Cancer: Guideline From the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and the American Society of Clinical Oncology. J Clin Oncol, 2017: p. JCO2016719807. Yamauchi, M., P. Lochhead, T. Morikawa, C. Huttenhower, A.T. Chan, E. Giovannucci, et al., Colorectal cancer: a tale of two sides or a continuum? Gut, 2012. 61(6): p. 794-7.

SC R

100.

A

112.

113.

22

Vitae Nele Boeckx has a master in the biomedical sciences and is working on her PhD with a focus on colorectal cancer, which is a collaboration between the Center of Medical Genetics (University of Antwerp (UA) / Antwerp University Hospital ( UZA)) and the Center of Oncological Research (UA). Katleen Janssens is an internal medicine (Oncology) intern. She graduated second of her year at the

IP T

UA and presented several posters on national and international congresses. She contributed to several projects in oncology and genetics.

Professor doctor Guy Van Camp is head of the ‘Human Molecular Genetics’ group in the Center of

is his group is focused on oncogenetics and sensory disorders.

SC R

Medical Genetics (UA/UZA) and board member of the Center of Oncological Research (UA). Research

Doctor Marika Rasschaert is head of oncology in AZ Monica Deurne and medical oncologist in the

U

UZA, specialized in digestive oncology.

N

Doctor Konstantinos Papadimitriou is a medical oncologist working at the UZA, specialized is

A

gastroenterological oncology.

M

Professor doctor Marc Peeters is head of the oncology department of the UZA, medical oncologist specialized in gastrointestinal oncology and board member of the Center of Oncological Research

ED

(UA).

Doctor Ken Op de Beeck is a postdoc in the field of oncogenetics in the Center of Medical Genetics

A

CC E

PT

(UA/UZA) and Center of Oncological Research (UA).

23

IP T SC R

A

CC E

PT

ED

M

A

N

U

Figure 1. Summary of the varying characteristics in right-sided and left-sided CRC CMS, consensus molecular subtype; MMR, mismatch repair

24

Table 1. Tumor features according to primary tumor location

Epidemiology

Left

Right

Higher incidence

Lower incidence Incidence increasing [7, 20-22]

Hindgut

Midgut

Vasculature

Inferior mesenteric artery

Superior mesenteric artery

Clinical characteristics

Mostly male [3]

Mostly female [2-5]

Younger [6, 7]

Older [2-9, 19]

Infiltrating, constricting lesion

Exophytic, polypoid lesion

Causing obstruction

Causing anemia [10-12]

Earlier diagnosis

Later diagnosis

SC R

IP T

Embryological origin

Higher TNM stage at diagnosis Larger tumors [6, 13]

Cancer syndrome

Familial adenomatous polyposis

Hereditary nonpolyposis CRC

Histology

Absorptive histology

Mucinous histology [3, 5, 8, 9, 13, 15-17, 19]

N

U

Smaller tumors

A

Signet-ring cell histology [3, 8, 13, 16]

More hepatic metastasis [3, 23]

M

Metastasis

More pulmonary [3, 8], bone [8, 9] and

central

nervous

Poor and undifferentiated histology [3, 5, 13, 17, 19] Increased risk of metachronous CRC [18] More peritoneal metastasis [8, 9, 23]

system

A

CC E

PT

ED

metastasis [8]

25

Table 2. Publications discussing the predictive value of tumor location Border Treatment Ref Trial R/L Population line Chemotherapy versus chemotherapy plus anti-EGFR therapy

[39] [33]

CRYSTAL

SF

RAS wt mCRC

1st line

3

PRIME

SF

RAS wt mCRC

1st line

3

TAILOR Wang et (2015)

SF

RAS wt mCRC

3

SF

mCRC

1st line 1st and 2nd line

.

FOLFIRI (51/138) FOLFOX (49/159) FOLFOX (38/162) CT (61/56; 44/49)1

2nd line

3

FOLFIRI (39/148)

FOLFIRI + cmab (33/142) FOLFOX + pmab (39/169) FOLFOX + cmab (45/146) CT + cmab (33/77; 28/68)1 FOLFIRI + pmab (31/150)

BSC (14/43)

BSC + (16/42)

pmab

3

BSC (27/45)

BSC + (29/60)

cmab

3

al.

[40]

20050181 SF RAS wt mCRC Best supportive care versus anti-EGFR therapy 20020408

SF

RAS wt mCRC later lines KRAS wt refractory [41] NCIC CO.17 SF, RTE mCRC later lines Chemotherapy versus chemotherapy plus anti-VEGF therapy He et al. (2017)

SF, RTE

mCRC

1st line

.

CT (58/86/99)

[15]

AVF2107g

SF

mCRC

1st line

3

CT (206/353)²

[15]

NO16966

SF

mCRC

1st line

3

2nd line

3

CT (333/935)² FOLFIRI (313/699)²

CT + bmab (78/86/80) CT + bmab (206/353)² CT + bmab (333/935)² FOLFIRI + rmab (313/699)²

FOLFIRI + cmab (38/157) FOLFOX + pmab (22/53) CT + cmab (26/41) CT + cmab (28/68)² CT + cmab (280/689)²

FOLFIRI + bmab (50/149) FOLFOX + bmab (14/54) CT + bmab (24/30) CT + bmab (28/68)² CT + bmab (280/689)²

M

mCRC

[31]

FIRE-3

SF

RAS wt mCRC

1st line

3

[38]

PEAK

SF

1st line

2

[30]

Lu et al. (2016) Sagawa et al. (2017) CALGB/SWOG 80405

RAS wt mCRC KRAS wt (exon 2) mCRC

1st line

.

mCRC KRAS wt (exon 2) mCRC

1st line

.

1st line

3

CC E

PT

ED

[43] RAISE SF Anti-EGFR versus anti-VEGF therapy

[44] [25] 1

N

[42]

A

U

[40]

Treatment arm 2 (R/L/(RT))

IP T

[38]

Treatment arm 1 (R/L/(RT))

SC R

[31]

Phase

SF, RTE SF

TC (E)

A

Numbers for respectively first- and second-line data ²Number of patients with left- and right-sided disease for both treatment arms, no separate data available anti-EGFR, anti-epidermal growth factor receptor; anti-VEGF, anti-vascular endothelial growth factor; bmab, bevacizumab; BSC, best supportive care; cmab, cetuximab; CT, chemotherapy; FOLFIRI, folinic acid (leucovorin), fluorouracil (5-FU) and irinotecan; FOLFOX, folinic acid (leucovorin), 5-FU and oxaliplatin; mCRC, metastatic colorectal cancer; pmab, panitumumab; R/L, Right/Left; R/L/(RT), Right/Left/(Rectum, if data available); Ref, Reference; rmab, ramucirumab; RTE, rectum excluded; SF, splenic flexure; TC (E), Transverse colon (excluded); wt, wild type. 26

Table 3. Overview of the different biomarkers in right-sided and left-sided colorectal cancer Biomarker Gut content

Right-sided CRC

Left-sided CRC

Fusobacterium nucleatum Carcinogenic bile acids Invasive polymicrobial biofilms

Bacterial load

Microsatellite instability Deficient MMR status

Chromosomal instability

IP T

Genomic instability

Epigenetic alterations CpG island methylation LINE-1 methylation

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Consensus molecular subtypes CMS1

CMS2

Mutations

NRAS TP53

U

KRAS BRAF PIK3CA

Epiregulin and amphiregulin

A

CC E

PT

ED

M

A

N

Gene expression

27