- Email: [email protected]
Meta-analysis for cyclin E in lung cancer survival
Clinica Chimica Acta 413 (2012) 663–668
Contents lists available at SciVerse ScienceDirect
Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim
Invited critical review
Meta-analysis for cyclin E in lung cancer survival Li-nian Huang a,⁎, 1, Dong-sheng Wang a, b, 1, Yu-qing Chen a, Wei Li a, Feng-dan Hu c, Bei-lei Gong a, Cheng-Ling Zhao a, Wei Jia a a b c
Department of Respiration, First Affiliated Hospital of Bengbu Medical College, Anhui Provincial Key Laboratory of Clinical Basic Research on Respiratory Disease, Bengbu, Anhui, China Department of Respiration, Anhui Provincial Hospital, Hefei, China Department of Respiration, Wuhe County Hospital, Anhui, China
a r t i c l e
i n f o
a b s t r a c t Background: To assess the prognosis value of cyclin E expression in survival of patients with lung cancer (LC), we performed a systematic review of the literature with meta-analysis. Methods: Electronic databases were used to identify published studies before August 2011. Pooled hazard ratio (HR) with 95% confidence interval (95% CI) was used to estimate the strength of the association of cyclin E expression with survival of LC patients. Heterogeneity and publication bias were also assessed. Results: Fourteen studies (2606 cases) were eligible and subjected to analysis. Cyclin E over-expression was found to be a strong predictor of poor prognosis in LC patients (HR: 1.38, 95% CI: 1.07–1.79; P = 0.014). When only non-small cell lung cancer (NSCLC) was considered, the combined HR was 1.53 (95% CI: 1.19–1.97, P = 0.001). A significant association was also evident when the analysis was limited to studies involving adenocarcinoma (AD), but not squamous cell carcinoma (SQ). Publication bias was absent. Sensitivity analyses suggested that the summary statistics obtained should approximate the actual average. © 2012 Elsevier B.V. All rights reserved.
Article history: Received 3 December 2011 Received in revised form 20 December 2011 Accepted 30 December 2011 Available online 9 January 2012 Keywords: Lung cancer Cyclin E Prognosis Meta-analysis
Contents 1. 2.
Introduction . . . . . . . . . . . . Methods . . . . . . . . . . . . . . 2.1. Identification of studies . . . 2.2. Data extraction . . . . . . . 2.3. Statistical analyses . . . . . 3. Results . . . . . . . . . . . . . . 3.1. Study characteristics . . . . 3.2. Overall results. . . . . . . . 3.3. Results of subgroup analyses . 3.4. Evaluation of publication bias 3.5. Sensitivity analysis . . . . . 4. Discussion . . . . . . . . . . . . . Conflict of interest statement . . . . . . Acknowledgment . . . . . . . . . . . . References . . . . . . . . . . . . . . .
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1. Introduction
⁎ Corresponding author at: Department of Respiration, First Affiliated Hospital of Bengbu Medical College, 287 Chang Huai Road, Bengbu, Anhui 233004, China. Tel.: +86 13855229506; fax: +86 552 3086132. E-mail address: [email protected] (L.N. Huang). 1 Contributed equally. 0009-8981/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cca.2011.12.020
Lung cancer (LC) remains the most frequent and the most lethal human malignancy, accounting for 1.1 million annual deaths worldwide [1,2]. LC is generally divided into small cell (SC) and non-small cell lung cancer (NSCLC). The latter accounts for ~ 85% of all cases of LC with adenocarcinoma (AD) accounting for ~ 40%, and squamous cell carcinoma (SQ) for ~ 35% [3]. Despite recent advances in surgery,
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Table 1 Characteristics of studies included in the meta-analysis. Author
Year
Type
Cyclin e(+)
Method
Cutoff
Stage
Histological type
HR estimation
Dobashi Y Fukuse Mishina T Anton R Muller-Tidow C Dosaka-Akita H Hayashi H Gao AF Takahashi S Dobashi Y Shou YN Yoo JY Filipits M Kosacka M
1998 2000 2000 2000 2001 2001 2001 2001 2002 2003 2007 2007 2007 2009
LC NSCLC NSCLC SQ NSCLC NSCLC AD NSCLC NSCLC LC NSCLC NSCLC NSCLC NSCLC
39/190 114/242 115/217 32/83 29/70 115/214 16/98 31/86 27/62 56/144 58/132 84/219 394/778 26/71
IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC
5% 20% NA 50% NA 30% 5% NA 5% 5% 10% 30% NA NA
NA I:98 II:30 IIIA:114 I:119 II:18 IIIA:72 IIIB:1 IV:7 I:58 II:25 1:37 II:13 IIIA:20 I:119 II:18 IIIA:72 IIIB:1 IV:7 NA NA NA I:52 II:48 IIIA:44 I:54, II:27, III:46, IV:5 I:135 II:25 III:59 I:268, II:180, III:330 I:29 II:14 IIIA:28
SQ:55 AD:58 SCC:36 LCC:41 SQ:85 AD:148 LCC:6 ADC:3 SQ:92 AD:107 Other:18 SQ:83 SQ:34 AD:26 LCC:10 SQ:92 AD:107 LCC:9 ADC:9 AD:98 SQ:54, AD:32 AD:36 SQ:26 AD:56 SQ:59 LCC:29 AD:86, SQ:38, ADC:3, LCC:5 AD:119 SQ:100 AD:249, SQ:432, Other:97 SQ:43 AD:17 LCC:6 Other:5
Survival curves HR + 95% CI HR + 95% CI Survival curves Survival curves HR + 95% CI HR + 95% CI HR + 95% CI HR + 95% CI HR + 95% CI Logrank + events HR + 95% CI HR + 95% CI Survival curves
LC: lung cancer; NSCLC: non-small cell lung cancer; IHC: Immunohistochemistry. SQ: Squamous cell cancer; AD: Adenocarcinoma; LCC: Large cell carcinoma. ADC: Adenosquamous carcinoma.
radiation and medical treatment, the overall five-year survival rate for LC is still less than 15% [4]. Prognosis remains difficult due to marked clinical heterogeneity even in those patients with similar staging. Substantial efforts have been made to identify prognostic factors to individualize treatment and improve survival. Many molecular markers, such as p16 [5], Bcl-2 [6], Ki-67 [7] and p27 [8], have been implicated both in the pathogenesis and prognosis of this disease. Recent studies of cell-cycle regulatory proteins have contributed to elucidating mechanisms of cancer development. Cyclins are prime cell cycle regulators and play a critical role in the control of cell proliferation by forming a complex with different cyclin-dependent kinases (CDKs). Cyclin E, which is expressed and associated with CDK2, plays
a critical role in the G1 phase and in the G1–S phase transition [9]. Abnormalities in cell-cycle regulators and subsequent deregulation of the G1/S transition may be one of the most important biologic events in the development and progression of cancer [10,11]. The clinicopathologic implications of cyclin E over-expression have been reported to involve in various types of cancer including breast [10], colon [12], bladder [13] and skin [14]. The expression of cyclin E in lung cancer patients has recently been studied. Dobashi et al. [15] reported that those patients whose tumors were cyclin E positive showed significantly increased survival rate than those without cyclin E expression. In contrast, Fukuse et al. [16] and Mishina et al. [17] reported that increased expression of cyclin E in LC tissue correlated
Fig. 1. Forest plot of meta-analysis of the effect of cyclin E expression on survival in LC patients.
L.N. Huang et al. / Clinica Chimica Acta 413 (2012) 663–668
with poorer prognosis. However, another study by Ikehara M et al. [18] suggested that increased expression of cyclin E was not associated with prognosis in LC. Because the prognostic value of cyclin E for survival in LC remains controversial, we performed a systematic review of the published literature with meta-analysis to clarify this point. 2. Methods 2.1. Identification of studies Meta-analysis was limited to studies dealing with the prognostic implications of different cyclin E protein expression level in the electronic PubMed and CNKI databases (to August 2011). References therein were also manually reviewed for articles potentially missed in the initial search. Search terms were “lung cancer”, “prognosis”, and “cyclin E”. Only Chinese and English language papers were included. Studies used in the meta-analysis had to meet the following inclusion criteria: cyclin E expression was evaluated in lung cancer; and hazard ratio (HR) and its confidence interval (CI) comparing patients with cyclin E expression with patients without expression were described or statistically extractable from data in the article. When duplicate articles were published, only the newest or most informative single article was selected. 2.2. Data extraction All the data were extracted independently by two reviewers using a standard protocol. Potential disagreements were resolved by
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consensus. The following characteristics were extracted: name of first author, year of publication, sample size, test method, cut-off value, tumor stage, histologic type and HR estimation. 2.3. Statistical analyses HR with 95% CI was used to combine the data. When described in original articles, these values were obtained directly. When these statistical variables were not provided, they were calculated from available numerical data or Kaplan–Meier survival curve. In these cases, after dividing the time axis into non-overlapping intervals, log HR and its variance for each interval were calculated. These estimated values were combined in a stratified manner to obtain the overall HR and 95% CI [19]. The individual HR estimates were combined into an overall HR using Peto's method [20], which consisted of a fixed-effect model assuming homogeneity of the individual true HRs. This assumption was tested by performing Chi-squared Q-tests for heterogeneity. A P-value greater than 0.05 for the Q-test indicated lack of heterogeneity among studies, so the fixed-effects model was used for meta-analysis. Otherwise, DerSimonian–Laird randomeffect method [21] was used. We also quantified the effect of heterogeneity using I 2 statistic which measured the degree of heterogeneity. I 2 value ranges from 0% to 100% (I 2 = 0–25%, no heterogeneity; I 2 = 25–50%, moderate heterogeneity; I 2 = 50–75%, large heterogeneity; I 2 = 75–100%, extreme heterogeneity) [22]. The potential publication bias was assessed using Begg's [23] and Egger's test [24]. All the statistical analyses were performed by Stata version 10 (StataCorp LP, College Station, TX, USA).
Fig. 2. Forest plot of meta-analysis of the effect of cyclin E expression on survival in NSCLC patients.
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3. Results 3.1. Study characteristics There were 63 papers (PubMed: 33, CNKI: 30) relevant to the search terms. A total of 48 papers were excluded (12 reviews, 2 animal studies, 4 not focused on LC, 30 not cyclin E expression). Of the remaining 15 papers, one paper [18] was excluded due to the insufficient data. Accordingly, 14 published studies [15–17,25–35] that included 2606 LC cases were considered in the meta-analysis (Table 1). 3.2. Overall results In the selected 14 papers, the estimated pooled HR was 1.38 (95% CI: 1.07–1.79; P = 0.014), suggesting that the positive expression of cyclin E was a strong predicator of poor prognostic among patients with LC. A significant heterogeneity was observed among studies (Q = 34.69, I 2 = 62.5%, P = 0.001), so it was possible to go further in categorizing the trials. Forest plot is shown (Fig. 1). 3.3. Results of subgroup analyses The subgroup analyses were performed according to histologic type. When the analysis of the studies was limited to investigating NSCLC, the combined HR was 1.53 (95% CI: 1.19–1.97, P = 0.001) with significant heterogeneity (Q = 26.19, P = 0.006, I 2 = 58.0%). We also focused on the predominant histologic type in each study. When the analysis was limited to AD studies in which AD
predominated, the pooled HR was 1.65 (95% CI: 1.31–2.07, P = 0.000) without heterogeneity (Q = 7.17, P = 0.208, I 2 = 30.3%). When the analysis was limited to studies focused on SQ, the pooled HR was 1.36 (95% CI: 0.80–2.31, P = 0.260) with significant heterogeneity (Q = 12.01, P = 0.007, I 2 = 75.0%). The Forest plots are shown (Figs. 2, 3 and 4). 3.4. Evaluation of publication bias Both Begg's funnel plot and Egger's test were performed to assess the publication bias. Begg's funnel plot did not reveal any evidence of obvious asymmetry in the overall meta-analysis (not shown). There was no indication of publication bias from either Egger's (P = 0.569) or Begg's (P = 0.412) tests. 3.5. Sensitivity analysis A sensitivity analysis, in which one study was removed at a time, was performed to evaluate result stability. The corresponding pooled HRs were not significantly altered, suggesting stability of our results (Table 2). 4. Discussion Several studies have indicated that patients with increased cyclin E expression had a poorer overall survival vs those with low expression. No consensus has been reached regarding whether cyclin E expression is a prognostic or predictive marker in LC, and cyclin E has
Fig. 3. Forest plot for 6 studies investigated mostly (> 50%) with adenocarcinomas.
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Fig. 4. Forest plot for 4 studies investigated mostly (> 50%) with squamous cell carcinomas.
attracted considerable attention. Meta-analysis was originally developed to combine the results of randomized controlled trials [20]. This approach has been successful in the identification of prognostic indicators such as Ki-67 [7] and epidermal growth factor receptor [36] in LC patients. Our meta-analysis, suggested that cyclin E overexpression had a poor survival (HR: 1.38, 95% CI: 1.07–1.79). When stratified by histologic type, we also found a significant association between cyclin E over-expression and poor survival in NSCLC patients, specifically AD. These findings might be important for prognosis and treatment of lung cancer, in addition to improve understanding of LC biology. Significant heterogeneity was detected among the studies included in the meta-analysis. Heterogeneity was still observed when we Table 2 Results of the sensitivity analyses. Excluded studies
HR (95% CI)
Dobashi Y et al. Fukuse et al. Mishina T et al. Anton R et al. Muller-Tidow C et al. Dosaka-Akita H et al. Hayashi H et al. Gao AF et al. Takahashi S et al. Dobashi Y et al. Shou YN et al. Yoo JY et al. Filipits M et al. Kosacka M et al.
1.47 1.34 1.34 1.43 1.37 1.34 1.39 1.31 1.36 1.44 1.32 1.44 1.45 1.37
(1.15–1.88) (1.02–1.76) (1.02–1.77) (1.09–1.87) (1.05–1.80) (1.03–1.76) (1.05–1.82) (1.02–1.69) (1.05–1.78) (1.10–1.88) (1.01–1.73) (1.10–1.89) (1.11–1.90) (1.05–1.80)
limited the scope of analysis to studies investigating NSCLC. When analysis was limited to AD studies, heterogeneity was not detected. When studies were limited to SQ, heterogeneity was still detected. Therefore, histologic type might be neither a major cause of heterogeneity nor a decisive factor in the biologic effect of cyclin E overexpression. The method of HR extrapolation requires comment. If not reported, HRs were calculated from the data available in the published article and, if this was not possible, extrapolated from the survival curves according to the method of Parmar et al. [19], implying assumptions on the censoring process. Although this approach might have been associated with errors due to imprecision of the reading, two independent reviewers were used to reduce this variation. Consequently, the estimated HR might be less reliable in comparison to published statistics. We compared our estimated HRs and their statistical significance with published results and did not identify any major contradiction. Publication bias is a well known problem in meta-analysis. Positive results tend to be accepted by journals while negative results are often rejected or not submitted. The review was restricted to papers published in English or Chinese, and language bias might exist. However, our analysis did not suggest publication bias, so the summary statistics obtained may approximate the actual average. Some limitations had to be considered in our study. First, tumor stage is likely an important prognostic indicator for LC. Unfortunately, we're not able to stratify by tumor stage because most studies did not provide sufficient information. Second, each study was not weighted by a quality score. Third, there was no common threshold in positive expression in assessment of survivin in LC patients, which might lead to heterogeneity.
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Despite of the limitations listed above, our study did find that cyclin E over-expression was associated with poor prognosis in LC, especially AD patients. Results were based on data obtained from retrospective trials and should be interpreted with caution. To become a useful prognostic marker for individual patients and in the context of targeted therapy, these results clearly need to be confirmed by well-designed clinical experiments with larger, more clearly defined patient populations. Conflict of interest statement None declared. Acknowledgment This work was partly supported by the grants from the Academic Leader Foundation of Anhui Provincial Health Department and the Doctor's Scientific Research Foundation of Bengbu Medical College. References [1] Boyle P, Dresler C. Preventing the lung cancer epidemic. Ann Oncol 2005 Oct;16(10):1565–6. [2] Witschi H. A short history of lung cancer. Toxicol Sci 2001;64(1):4–6. [3] Esposito L, Conti D, Ailavajhala R, Khalil N, Giordano A. Lung cancer: are we up to the challenge? Curr Genomics 2010;11(7):513–8. [4] Cox G, Jones JL, Andi A, Waller DA, O'Byrne. A biological staging model for operable non-small cell lung cancer. Thorax 2001;56:561–6. [5] Tong J, Sun X, Cheng H, Zhao D, Ma J, Zhen Q, et al. Expression of p16 in non-small cell lung cancer and its prognosis significance: a meta-analysis of published literatures. Lung Cancer 2011;74:155–63. [6] Martin B, Paesmans M, Berghmans T, Branle F, Ghisdal L, Mascaux C, et al. Role of Bcl-2 as a prognostic factor for survival in lung cancer: a systematic review of the literature with meta-analysis. Br J Cancer 2003;89(1):55–64. [7] Martin B, Paesmans M, Mascaux C, Berghmans T, Lothaire P, Meert AP, et al. Ki-67 expression and patients survival in lung cancer: systematic review of the literature with meta-analysis. Br J Cancer 2004;91(12):2018–25. [8] Zhuang Y, Yin HT, Yin XL, Wang J, Zhang DP. High p27 expression is associated with a better prognosis in East Asian non-small cell lung cancer patients. Clin Chim Acta 2011;412(23–24):2228–31. [9] Pines J, Hunter T. Isolation of a human cyclin cDNA: evidence for cyclin mRNA and protein regulation in the cell cycle for interaction with p34cdc2. Cell 1989;58: 833–46. [10] Keyomarsi K, O'Leary N, Molnar G, Lees E, Fingert HJ, Pardee AB. Cyclin E, a potential prognostic marker for breast cancer. Cancer Res 1994;54:380–5. [11] Dutta A, Chandra R, Leiter LM, Lester S. Cyclins as markers of tumor proliferation: immunohistochemical studies in breast cancer. Proc Natl Acad Sci U S A 1995;92: 5386–90. [12] Kitahara K, Yasui W, Kuniyasu H, Yokozaki H, Akama Y, Yunotani S, et al. Concurrent amplification of cyclin E and cdk2 genes in colorectal carcinomas. Int J Cancer 1995;62:25–8. [13] Del Pizzo J, Borkowski A, Jacobs SC, Kyprianou N. Loss of cell cycle regulators in p27 (Kip1) and cyclin E in transitional cell carcinoma of the bladder correlates with tumor grade and patient survival. Am J Pathol 1999;155:1129–36. [14] Bito T, Ueda M, Ito A, Ichihashi M. Less expression of cyclin E in cutaneous squamous cell carcinomas than in benign and premalignant keratinocytic lesions. J Cutan Pathol 1997;24:305–8. [15] Dobashi Y, Shoji M, Jiang SX, Kobayashi M, Kawakubo Y, Kameya T. Active cyclin A-CDK2 complex, a possible critical factor for cell proliferation in human primary lung carcinomas. Am J Pathol 1998 Sep;153(3):963–72.
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Contents lists available at SciVerse ScienceDirect
Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim
Invited critical review
Meta-analysis for cyclin E in lung cancer survival Li-nian Huang a,⁎, 1, Dong-sheng Wang a, b, 1, Yu-qing Chen a, Wei Li a, Feng-dan Hu c, Bei-lei Gong a, Cheng-Ling Zhao a, Wei Jia a a b c
Department of Respiration, First Affiliated Hospital of Bengbu Medical College, Anhui Provincial Key Laboratory of Clinical Basic Research on Respiratory Disease, Bengbu, Anhui, China Department of Respiration, Anhui Provincial Hospital, Hefei, China Department of Respiration, Wuhe County Hospital, Anhui, China
a r t i c l e
i n f o
a b s t r a c t Background: To assess the prognosis value of cyclin E expression in survival of patients with lung cancer (LC), we performed a systematic review of the literature with meta-analysis. Methods: Electronic databases were used to identify published studies before August 2011. Pooled hazard ratio (HR) with 95% confidence interval (95% CI) was used to estimate the strength of the association of cyclin E expression with survival of LC patients. Heterogeneity and publication bias were also assessed. Results: Fourteen studies (2606 cases) were eligible and subjected to analysis. Cyclin E over-expression was found to be a strong predictor of poor prognosis in LC patients (HR: 1.38, 95% CI: 1.07–1.79; P = 0.014). When only non-small cell lung cancer (NSCLC) was considered, the combined HR was 1.53 (95% CI: 1.19–1.97, P = 0.001). A significant association was also evident when the analysis was limited to studies involving adenocarcinoma (AD), but not squamous cell carcinoma (SQ). Publication bias was absent. Sensitivity analyses suggested that the summary statistics obtained should approximate the actual average. © 2012 Elsevier B.V. All rights reserved.
Article history: Received 3 December 2011 Received in revised form 20 December 2011 Accepted 30 December 2011 Available online 9 January 2012 Keywords: Lung cancer Cyclin E Prognosis Meta-analysis
Contents 1. 2.
Introduction . . . . . . . . . . . . Methods . . . . . . . . . . . . . . 2.1. Identification of studies . . . 2.2. Data extraction . . . . . . . 2.3. Statistical analyses . . . . . 3. Results . . . . . . . . . . . . . . 3.1. Study characteristics . . . . 3.2. Overall results. . . . . . . . 3.3. Results of subgroup analyses . 3.4. Evaluation of publication bias 3.5. Sensitivity analysis . . . . . 4. Discussion . . . . . . . . . . . . . Conflict of interest statement . . . . . . Acknowledgment . . . . . . . . . . . . References . . . . . . . . . . . . . . .
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1. Introduction
⁎ Corresponding author at: Department of Respiration, First Affiliated Hospital of Bengbu Medical College, 287 Chang Huai Road, Bengbu, Anhui 233004, China. Tel.: +86 13855229506; fax: +86 552 3086132. E-mail address: [email protected] (L.N. Huang). 1 Contributed equally. 0009-8981/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cca.2011.12.020
Lung cancer (LC) remains the most frequent and the most lethal human malignancy, accounting for 1.1 million annual deaths worldwide [1,2]. LC is generally divided into small cell (SC) and non-small cell lung cancer (NSCLC). The latter accounts for ~ 85% of all cases of LC with adenocarcinoma (AD) accounting for ~ 40%, and squamous cell carcinoma (SQ) for ~ 35% [3]. Despite recent advances in surgery,
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Table 1 Characteristics of studies included in the meta-analysis. Author
Year
Type
Cyclin e(+)
Method
Cutoff
Stage
Histological type
HR estimation
Dobashi Y Fukuse Mishina T Anton R Muller-Tidow C Dosaka-Akita H Hayashi H Gao AF Takahashi S Dobashi Y Shou YN Yoo JY Filipits M Kosacka M
1998 2000 2000 2000 2001 2001 2001 2001 2002 2003 2007 2007 2007 2009
LC NSCLC NSCLC SQ NSCLC NSCLC AD NSCLC NSCLC LC NSCLC NSCLC NSCLC NSCLC
39/190 114/242 115/217 32/83 29/70 115/214 16/98 31/86 27/62 56/144 58/132 84/219 394/778 26/71
IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC IHC
5% 20% NA 50% NA 30% 5% NA 5% 5% 10% 30% NA NA
NA I:98 II:30 IIIA:114 I:119 II:18 IIIA:72 IIIB:1 IV:7 I:58 II:25 1:37 II:13 IIIA:20 I:119 II:18 IIIA:72 IIIB:1 IV:7 NA NA NA I:52 II:48 IIIA:44 I:54, II:27, III:46, IV:5 I:135 II:25 III:59 I:268, II:180, III:330 I:29 II:14 IIIA:28
SQ:55 AD:58 SCC:36 LCC:41 SQ:85 AD:148 LCC:6 ADC:3 SQ:92 AD:107 Other:18 SQ:83 SQ:34 AD:26 LCC:10 SQ:92 AD:107 LCC:9 ADC:9 AD:98 SQ:54, AD:32 AD:36 SQ:26 AD:56 SQ:59 LCC:29 AD:86, SQ:38, ADC:3, LCC:5 AD:119 SQ:100 AD:249, SQ:432, Other:97 SQ:43 AD:17 LCC:6 Other:5
Survival curves HR + 95% CI HR + 95% CI Survival curves Survival curves HR + 95% CI HR + 95% CI HR + 95% CI HR + 95% CI HR + 95% CI Logrank + events HR + 95% CI HR + 95% CI Survival curves
LC: lung cancer; NSCLC: non-small cell lung cancer; IHC: Immunohistochemistry. SQ: Squamous cell cancer; AD: Adenocarcinoma; LCC: Large cell carcinoma. ADC: Adenosquamous carcinoma.
radiation and medical treatment, the overall five-year survival rate for LC is still less than 15% [4]. Prognosis remains difficult due to marked clinical heterogeneity even in those patients with similar staging. Substantial efforts have been made to identify prognostic factors to individualize treatment and improve survival. Many molecular markers, such as p16 [5], Bcl-2 [6], Ki-67 [7] and p27 [8], have been implicated both in the pathogenesis and prognosis of this disease. Recent studies of cell-cycle regulatory proteins have contributed to elucidating mechanisms of cancer development. Cyclins are prime cell cycle regulators and play a critical role in the control of cell proliferation by forming a complex with different cyclin-dependent kinases (CDKs). Cyclin E, which is expressed and associated with CDK2, plays
a critical role in the G1 phase and in the G1–S phase transition [9]. Abnormalities in cell-cycle regulators and subsequent deregulation of the G1/S transition may be one of the most important biologic events in the development and progression of cancer [10,11]. The clinicopathologic implications of cyclin E over-expression have been reported to involve in various types of cancer including breast [10], colon [12], bladder [13] and skin [14]. The expression of cyclin E in lung cancer patients has recently been studied. Dobashi et al. [15] reported that those patients whose tumors were cyclin E positive showed significantly increased survival rate than those without cyclin E expression. In contrast, Fukuse et al. [16] and Mishina et al. [17] reported that increased expression of cyclin E in LC tissue correlated
Fig. 1. Forest plot of meta-analysis of the effect of cyclin E expression on survival in LC patients.
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with poorer prognosis. However, another study by Ikehara M et al. [18] suggested that increased expression of cyclin E was not associated with prognosis in LC. Because the prognostic value of cyclin E for survival in LC remains controversial, we performed a systematic review of the published literature with meta-analysis to clarify this point. 2. Methods 2.1. Identification of studies Meta-analysis was limited to studies dealing with the prognostic implications of different cyclin E protein expression level in the electronic PubMed and CNKI databases (to August 2011). References therein were also manually reviewed for articles potentially missed in the initial search. Search terms were “lung cancer”, “prognosis”, and “cyclin E”. Only Chinese and English language papers were included. Studies used in the meta-analysis had to meet the following inclusion criteria: cyclin E expression was evaluated in lung cancer; and hazard ratio (HR) and its confidence interval (CI) comparing patients with cyclin E expression with patients without expression were described or statistically extractable from data in the article. When duplicate articles were published, only the newest or most informative single article was selected. 2.2. Data extraction All the data were extracted independently by two reviewers using a standard protocol. Potential disagreements were resolved by
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consensus. The following characteristics were extracted: name of first author, year of publication, sample size, test method, cut-off value, tumor stage, histologic type and HR estimation. 2.3. Statistical analyses HR with 95% CI was used to combine the data. When described in original articles, these values were obtained directly. When these statistical variables were not provided, they were calculated from available numerical data or Kaplan–Meier survival curve. In these cases, after dividing the time axis into non-overlapping intervals, log HR and its variance for each interval were calculated. These estimated values were combined in a stratified manner to obtain the overall HR and 95% CI [19]. The individual HR estimates were combined into an overall HR using Peto's method [20], which consisted of a fixed-effect model assuming homogeneity of the individual true HRs. This assumption was tested by performing Chi-squared Q-tests for heterogeneity. A P-value greater than 0.05 for the Q-test indicated lack of heterogeneity among studies, so the fixed-effects model was used for meta-analysis. Otherwise, DerSimonian–Laird randomeffect method [21] was used. We also quantified the effect of heterogeneity using I 2 statistic which measured the degree of heterogeneity. I 2 value ranges from 0% to 100% (I 2 = 0–25%, no heterogeneity; I 2 = 25–50%, moderate heterogeneity; I 2 = 50–75%, large heterogeneity; I 2 = 75–100%, extreme heterogeneity) [22]. The potential publication bias was assessed using Begg's [23] and Egger's test [24]. All the statistical analyses were performed by Stata version 10 (StataCorp LP, College Station, TX, USA).
Fig. 2. Forest plot of meta-analysis of the effect of cyclin E expression on survival in NSCLC patients.
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3. Results 3.1. Study characteristics There were 63 papers (PubMed: 33, CNKI: 30) relevant to the search terms. A total of 48 papers were excluded (12 reviews, 2 animal studies, 4 not focused on LC, 30 not cyclin E expression). Of the remaining 15 papers, one paper [18] was excluded due to the insufficient data. Accordingly, 14 published studies [15–17,25–35] that included 2606 LC cases were considered in the meta-analysis (Table 1). 3.2. Overall results In the selected 14 papers, the estimated pooled HR was 1.38 (95% CI: 1.07–1.79; P = 0.014), suggesting that the positive expression of cyclin E was a strong predicator of poor prognostic among patients with LC. A significant heterogeneity was observed among studies (Q = 34.69, I 2 = 62.5%, P = 0.001), so it was possible to go further in categorizing the trials. Forest plot is shown (Fig. 1). 3.3. Results of subgroup analyses The subgroup analyses were performed according to histologic type. When the analysis of the studies was limited to investigating NSCLC, the combined HR was 1.53 (95% CI: 1.19–1.97, P = 0.001) with significant heterogeneity (Q = 26.19, P = 0.006, I 2 = 58.0%). We also focused on the predominant histologic type in each study. When the analysis was limited to AD studies in which AD
predominated, the pooled HR was 1.65 (95% CI: 1.31–2.07, P = 0.000) without heterogeneity (Q = 7.17, P = 0.208, I 2 = 30.3%). When the analysis was limited to studies focused on SQ, the pooled HR was 1.36 (95% CI: 0.80–2.31, P = 0.260) with significant heterogeneity (Q = 12.01, P = 0.007, I 2 = 75.0%). The Forest plots are shown (Figs. 2, 3 and 4). 3.4. Evaluation of publication bias Both Begg's funnel plot and Egger's test were performed to assess the publication bias. Begg's funnel plot did not reveal any evidence of obvious asymmetry in the overall meta-analysis (not shown). There was no indication of publication bias from either Egger's (P = 0.569) or Begg's (P = 0.412) tests. 3.5. Sensitivity analysis A sensitivity analysis, in which one study was removed at a time, was performed to evaluate result stability. The corresponding pooled HRs were not significantly altered, suggesting stability of our results (Table 2). 4. Discussion Several studies have indicated that patients with increased cyclin E expression had a poorer overall survival vs those with low expression. No consensus has been reached regarding whether cyclin E expression is a prognostic or predictive marker in LC, and cyclin E has
Fig. 3. Forest plot for 6 studies investigated mostly (> 50%) with adenocarcinomas.
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Fig. 4. Forest plot for 4 studies investigated mostly (> 50%) with squamous cell carcinomas.
attracted considerable attention. Meta-analysis was originally developed to combine the results of randomized controlled trials [20]. This approach has been successful in the identification of prognostic indicators such as Ki-67 [7] and epidermal growth factor receptor [36] in LC patients. Our meta-analysis, suggested that cyclin E overexpression had a poor survival (HR: 1.38, 95% CI: 1.07–1.79). When stratified by histologic type, we also found a significant association between cyclin E over-expression and poor survival in NSCLC patients, specifically AD. These findings might be important for prognosis and treatment of lung cancer, in addition to improve understanding of LC biology. Significant heterogeneity was detected among the studies included in the meta-analysis. Heterogeneity was still observed when we Table 2 Results of the sensitivity analyses. Excluded studies
HR (95% CI)
Dobashi Y et al. Fukuse et al. Mishina T et al. Anton R et al. Muller-Tidow C et al. Dosaka-Akita H et al. Hayashi H et al. Gao AF et al. Takahashi S et al. Dobashi Y et al. Shou YN et al. Yoo JY et al. Filipits M et al. Kosacka M et al.
1.47 1.34 1.34 1.43 1.37 1.34 1.39 1.31 1.36 1.44 1.32 1.44 1.45 1.37
(1.15–1.88) (1.02–1.76) (1.02–1.77) (1.09–1.87) (1.05–1.80) (1.03–1.76) (1.05–1.82) (1.02–1.69) (1.05–1.78) (1.10–1.88) (1.01–1.73) (1.10–1.89) (1.11–1.90) (1.05–1.80)
limited the scope of analysis to studies investigating NSCLC. When analysis was limited to AD studies, heterogeneity was not detected. When studies were limited to SQ, heterogeneity was still detected. Therefore, histologic type might be neither a major cause of heterogeneity nor a decisive factor in the biologic effect of cyclin E overexpression. The method of HR extrapolation requires comment. If not reported, HRs were calculated from the data available in the published article and, if this was not possible, extrapolated from the survival curves according to the method of Parmar et al. [19], implying assumptions on the censoring process. Although this approach might have been associated with errors due to imprecision of the reading, two independent reviewers were used to reduce this variation. Consequently, the estimated HR might be less reliable in comparison to published statistics. We compared our estimated HRs and their statistical significance with published results and did not identify any major contradiction. Publication bias is a well known problem in meta-analysis. Positive results tend to be accepted by journals while negative results are often rejected or not submitted. The review was restricted to papers published in English or Chinese, and language bias might exist. However, our analysis did not suggest publication bias, so the summary statistics obtained may approximate the actual average. Some limitations had to be considered in our study. First, tumor stage is likely an important prognostic indicator for LC. Unfortunately, we're not able to stratify by tumor stage because most studies did not provide sufficient information. Second, each study was not weighted by a quality score. Third, there was no common threshold in positive expression in assessment of survivin in LC patients, which might lead to heterogeneity.
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Despite of the limitations listed above, our study did find that cyclin E over-expression was associated with poor prognosis in LC, especially AD patients. Results were based on data obtained from retrospective trials and should be interpreted with caution. To become a useful prognostic marker for individual patients and in the context of targeted therapy, these results clearly need to be confirmed by well-designed clinical experiments with larger, more clearly defined patient populations. Conflict of interest statement None declared. Acknowledgment This work was partly supported by the grants from the Academic Leader Foundation of Anhui Provincial Health Department and the Doctor's Scientific Research Foundation of Bengbu Medical College. References [1] Boyle P, Dresler C. Preventing the lung cancer epidemic. Ann Oncol 2005 Oct;16(10):1565–6. [2] Witschi H. A short history of lung cancer. Toxicol Sci 2001;64(1):4–6. [3] Esposito L, Conti D, Ailavajhala R, Khalil N, Giordano A. Lung cancer: are we up to the challenge? Curr Genomics 2010;11(7):513–8. [4] Cox G, Jones JL, Andi A, Waller DA, O'Byrne. A biological staging model for operable non-small cell lung cancer. Thorax 2001;56:561–6. [5] Tong J, Sun X, Cheng H, Zhao D, Ma J, Zhen Q, et al. Expression of p16 in non-small cell lung cancer and its prognosis significance: a meta-analysis of published literatures. Lung Cancer 2011;74:155–63. [6] Martin B, Paesmans M, Berghmans T, Branle F, Ghisdal L, Mascaux C, et al. Role of Bcl-2 as a prognostic factor for survival in lung cancer: a systematic review of the literature with meta-analysis. Br J Cancer 2003;89(1):55–64. [7] Martin B, Paesmans M, Mascaux C, Berghmans T, Lothaire P, Meert AP, et al. Ki-67 expression and patients survival in lung cancer: systematic review of the literature with meta-analysis. Br J Cancer 2004;91(12):2018–25. [8] Zhuang Y, Yin HT, Yin XL, Wang J, Zhang DP. High p27 expression is associated with a better prognosis in East Asian non-small cell lung cancer patients. Clin Chim Acta 2011;412(23–24):2228–31. [9] Pines J, Hunter T. Isolation of a human cyclin cDNA: evidence for cyclin mRNA and protein regulation in the cell cycle for interaction with p34cdc2. Cell 1989;58: 833–46. [10] Keyomarsi K, O'Leary N, Molnar G, Lees E, Fingert HJ, Pardee AB. Cyclin E, a potential prognostic marker for breast cancer. Cancer Res 1994;54:380–5. [11] Dutta A, Chandra R, Leiter LM, Lester S. Cyclins as markers of tumor proliferation: immunohistochemical studies in breast cancer. Proc Natl Acad Sci U S A 1995;92: 5386–90. [12] Kitahara K, Yasui W, Kuniyasu H, Yokozaki H, Akama Y, Yunotani S, et al. Concurrent amplification of cyclin E and cdk2 genes in colorectal carcinomas. Int J Cancer 1995;62:25–8. [13] Del Pizzo J, Borkowski A, Jacobs SC, Kyprianou N. Loss of cell cycle regulators in p27 (Kip1) and cyclin E in transitional cell carcinoma of the bladder correlates with tumor grade and patient survival. Am J Pathol 1999;155:1129–36. [14] Bito T, Ueda M, Ito A, Ichihashi M. Less expression of cyclin E in cutaneous squamous cell carcinomas than in benign and premalignant keratinocytic lesions. J Cutan Pathol 1997;24:305–8. [15] Dobashi Y, Shoji M, Jiang SX, Kobayashi M, Kawakubo Y, Kameya T. Active cyclin A-CDK2 complex, a possible critical factor for cell proliferation in human primary lung carcinomas. Am J Pathol 1998 Sep;153(3):963–72.
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