Adenocarcinoma in situ, minimally invasive adenocarcinoma, and invasive pulmonary adenocarcinoma—analysis of interobserver agreement, survival, radiographic characteristics, and gross pathology in 296 nodules

Human Pathology (2016) 51, 41–50

www.elsevier.com/locate/humpath

Original contribution

Adenocarcinoma in situ, minimally invasive adenocarcinoma, and invasive pulmonary adenocarcinoma—analysis of interobserver agreement, survival, radiographic characteristics, and gross pathology in 296 nodules☆ Jennifer M. Boland MD a,⁎, Adam T. Froemming MD b , Jason A. Wampfler BS d , Fabien Maldonado MD c , Tobias Peikert MD c , Courtney Hyland PA a , Mariza de Andrade PhD d , Marie Christine Aubry MD a , Ping Yang MD, PhD e , Eunhee S. Yi MD a a

Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, 55905 Department of Radiology, Mayo Clinic, Rochester, MN, 55905 c Department of Pulmonology and Critical Care Medicine, Mayo Clinic, Rochester, MN, 55905 d Department of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN, 55905 e Department of Epidemiology, Mayo Clinic, Rochester, MN, 55905 b

Received 8 October 2015; revised 3 December 2015; accepted 11 December 2015

Keywords: Agreement; Minimally invasive adenocarcinoma; MIA; AIS; Survival

Summary The International Association for the Study of Lung Cancer/American Thoracic Society/ European Respiratory Society and 2015 World Health Organization classifications of lung adenocarcinoma recommend designating tumors showing entirely lepidic growth as adenocarcinoma in situ (AIS) and lepidic tumors with invasion less than or equal to 5 mm as minimally invasive adenocarcinoma (MIA), both of which have superior outcome to conventional invasive adenocarcinoma (IA). Data on interobserver variability within this classification are limited, and further validation of the superior survival of AIS and MIA is needed. A total of 296 surgically excised pulmonary adenocarcinomas were reviewed from 254 patients (1997-2009). Slides were independently reviewed by 2 pulmonary pathologists who categorized tumors as AIS, MIA, or IA. Of 296 nodules, 244 (82.4%) were agreed upon by both observers: 10 AIS, 61 MIA, and 173 IA (κ = 0.63, good agreement). In 6 cases (2%), there was disagreement between AIS and MIA; in 45 cases (15%), there was disagreement between MIA and IA; and in 1 case, there was disagreement between AIS and IA. Overall survival was significantly different among categories as determined by both observers. Cases with disagreement between MIA and IA had similar survival to agreed MIA. Disease-specific 10-year survival was 100%

☆

Disclosures: No disclosures and grant support. ⁎ Corresponding author at: Mayo Clinic, Division of Anatomic Pathology, 200 1st Street SW, Rochester, MN 55905. E-mail address: [email protected] (J. M. Boland).

http://dx.doi.org/10.1016/j.humpath.2015.12.010 0046-8177/© 2016 Elsevier Inc. All rights reserved.

42

J. M. Boland et al. for AIS (both observers) and 97.3% and 97.6% for MIA, although this did not reach statistical significance compared to IA for either observer. Good agreement was present between observers when classifying tumors as AIS, MIA, and IA. Significant differences in overall survival were present between the 3 groups for both observers, and interobserver variability was evident. Patients with AIS and MIA experienced excellent DSS. © 2016 Elsevier Inc. All rights reserved.

1. Introduction Historically, pulmonary adenocarcinomas with lepidic growth (growth along alveolar septa) have been termed bronchioloalveolar carcinoma (BAC), a term coined by Dr Averill Liebow in 1960 [1]. He noted that BAC had an indolent clinical course compared to other aggressive types of lung cancer [1]. The definition of BAC was made more stringent over the years and was eventually defined as a tumor showing entirely lepidic growth without invasion [2-4]. Subsequent studies focused on small lepidicpredominant tumors with limited areas of invasion, which have shown that the size of invasion or scarring may be more prognostic than gross tumor size [2,3,5-8]. Tumors with less than or equal to 5 mm of invasion are associated with excellent survival and have been termed minimally invasive adenocarcinoma (MIA) [3,5]. A consensus classification was proposed by the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society in 2011, which has been adopted by the 2015 World Health Organization (WHO) classification of pulmonary adenocarcinoma [9,10]. This classification abandons the term BAC in favor of adenocarcinoma in situ (AIS) and formally introduces MIA as a diagnostic category, whereas tumors with greater than 5 mm invasion are classified as invasive adenocarcinoma (IA) [9,10]. AIS and MIA are limited to tumors less than or equal to 3 cm because data on larger tumors are very limited. Studies have shown that solid and micropapillary tumors are more aggressive, whereas lepidic tumors have better survival [11-19], so it is also recommended that IAs be subclassified according to the predominant histologic pattern. The proportion of adenocarcinomas classified as AIS or MIA will likely grow in the immediate future. Because AIS/ MIA are small and asymptomatic, they are the tumors most likely to be detected by imaging procedures done for other reasons. The number of detected nodules will increase due to the favorable results of the National Lung Cancer Screening Trial [20], and most screening-detected lung cancers are adenocarcinomas. These factors will lead to more incidentally discovered adenocarcinomas: some would have gone undiagnosed in the past (“overdiagnosed” cancers, indolent tumors that would not have caused the patient's death), and some may be discovered at earlier stage with a more significant lepidic component. Little is known about interobserver agreement when classifying tumors as AIS, MIA, and IA [5,21]. Most

agreement studies focus on predominant invasive pattern [18,22,23]. Preliminary validation studies of the new classification have been promising [13,15,17,24-28], but further validation of the superior survival of patients with AIS/MIA is needed. AIS/MIA are uncommon and often constitute a small minority of tumors even in large studies, especially among Western patient populations [12,13,17,28]. Furthermore, the behavior of tumors in which there is disagreement between invasive categories determined by different observers is unknown. The goal of this study is to evaluate a large number of pulmonary adenocarcinomas enriched for AIS and MIA, to compare categorization between 2 observers, and to correlate invasive group with outcome.

2. Materials and methods The protocol was approved by the Mayo Clinic Institutional Review Board. Patients were selected from the Mayo Clinic Epidemiology and Genetics of Lung Cancer Study database, who underwent surgical resection of pulmonary adenocarcinoma (1997-2009). Cases were enriched for AIS and MIA by selecting cases to review which had the term BAC or adenocarcinoma with BAC features in the original diagnostic line. A total of 296 nodules were reviewed from 254 nonconsecutive patients. Thirty-five patients had more than 1 nodule (range, 2-5). Pathology slides were reviewed and independently evaluated by 2 pulmonary pathologists (E. S. Y. and J. M. B.), blinded to gross size, stage, and outcome. The pathologists used published 2015 WHO/2011 International Association for the Study of Lung Cancer/American Thoracic Society/ European Respiratory Society criteria, applied independently by each reviewer [9,10]. Each pathologist determined foci of stromal, vascular, and pleural invasion. The largest single focus of invasion and central scar (if present) were measured with a ruler. If a tumor was entirely IA, invasive size was considered equivalent to gross size. Tumors were categorized as AIS, MIA, or IA per 2015 WHO criteria. If the patient had multiple nodules that were felt to represent independent primaries after comprehensive histologic comparison of the nodules and evaluation for extent of lepidic growth, the tumors were independently evaluated for largest invasive tumor size and included in the interobserver agreement data set. If a tumor was categorized as AIS or MIA by one or both pathologists, residual gross pathology specimens were

Interobserver agreement in pulmonary adenocarcinoma classification examined by a pathologist assistant (C. H.) for all cases diagnosed since 2002 (62 patients; earlier cases had already been discarded). Any suspected residual tumor was submitted for histology. Only 2 cases with gross residual tumor originally had multiple nodules, and the identity of the nodules could be confirmed because of the proximity to the pleura (1 nodule subpleural, 1 parenchymal) or the involvement of separate lobes. All cases categorized as AIS or MIA with preoperative computed tomographic (CT) examinations were reviewed by a radiologist (A. T. F.) to determine radiologic size. Cases that could not be accurately measured were excluded (obscuring consolidation, multiple nodules without confident correlation between the sampled lesion and a specific nodule at imaging). Radiographic size was determined in 91 nodules from 82 patients. Each tumor was categorized as a ground glass opacity (GGO), subsolid, or solid. Follow-up information was extracted from medical records and Epidemiology and Genetics of Lung Cancer Study questionnaires. Disease-specific survival (DSS) information was extracted on 122 patients with nonmultifocal stage I tumors without prior history of lung cancer, with complete clinical follow-up, confirmed vital status, and cause of death (if applicable). Descriptive statistics using χ2 and Kruskal-Wallis tests were used as needed. Simple and weighted κ coefficients were used to assess agreement for classifying tumors as AIS, MIA, or IA. κ Values of 0.41 to 0.60 were moderate; 0.61 to 0.80, good; and 0.81 to 0.99, excellent. Intraclass correlation coefficients (ICCs) were used to evaluate the reliability of measurements of scar and invasion sizes. ICC values of 0.60 to 0.70 were good; and 0.75-1.00, excellent. Survival differences by tumor classification were analyzed for each pathologist's observations. If the patient had more than 1 nodule, comprehensive histologic comparison of the nodules with consideration of extent of lepidic growth and morphologic pattern similarity was used determine whether the nodules represented independent primaries or intrapulmonary metastases for staging purposes. If the nodules were felt to be independent primaries, the nodule with the largest invasive size was used to assign invasive category for survival analysis. Log-rank tests and KaplanMeier estimates were used to test for survival differences and estimate survival percentages, respectively. Univariate and multivariate Cox proportional hazards models were used to assess overall survival (OS) and DSS. Multivariate models were constructed via a stepwise procedure using a 0.1 significance level for variable entry and removal. Ten covariates were considered in the model selection process: age, sex, race, smoking status, stage, grade, surgery, chemotherapy, radiation, and lung cancer history. Grade was determined by a pulmonary pathologist, with each tumor designated as well, moderately or poorly differentiated based on overall impression incorporating factors such as observed growth patterns, nuclear atypia, and necrosis.

43

3. Results 3.1. Demographics A total of 296 nodules were evaluated from 254 patients (153 females, 60%; see Table 1). Most patients (233) were white (92%), with 150 former smokers (59%), 44 current smokers (17%), and 60 never smokers (24%). Average age was 68.3 years (17-91). Most patients (190, 75%) were stage I, whereas 36 were stage II (14%); 23, stage III (9%); and 5, stage IV (2%). Average gross nodule size was 2.0 cm (0.2-17). Average number of slides reviewed per case was 3.9 (1-132; median, 3).

3.2. Gross examination of residual tissue Examination of the gross residual tissue was performed for 62 patients with tumors categorized initially as AIS or MIA by one or both observers. In 27 patients (44%), no gross residual lesion was identified. Sections were submitted in 35 cases (56%), ranging from 1 to 127 slides (average, 6.4; median, 1; mode, 1). In 3 patients (9%), submitted tissue was not tumor. In 25 patients (71%), examination of the residual

Table 1

Summary of demographic data for 254 study patients No. of patients (%) (n = 254)

Age at diagnosis Mean (SD) 68.3 (10.4) Median 69.5 Range 17-91 Sex Female 153 (60.2%) Male 101 (39.8%) Race White 233 (92.1%) Other 20 (7.9%) Unknown 1 (0.4%) Smoking status Never 60 (23.6%) Former 150 (59.1%) Current 44 (17.3%) Stage (AJCC 2009) I 190 (74.8%) II 36 (14.2%) III 23 (9.1%) IV 5 (2.0%) Lung cancer progression No 207 (81.5%) Yes 47 (18.5%) Treatment modality Only surgery 194 (76.4%) Surgery and chemo/radiation 52 (20.5%) Other/none/unknown 8 (3.1%) Abbreviation: AJCC, American Joint Committee on Cancer.

44

J. M. Boland et al.

Table 2 Comparison of 3-level and 2-level invasion category ratings between 2 observers (n=296 tumors) Observer 2 3-level System AIS Observer 1 AIS MIA IA

MIA

10 (3.4%) 5 (1.7%) 1 (0.3%)

IA

1 (0.3%) 0 (0.0%) 61 (20.6%) 13 (4.4%) 32 (10.8%) 173 (58.5%)

2-level System AIS/MIA

(range, 3.2-5.5 cm), and the AIS was 3.5 cm. Examination of gross residual tumor was possible in 7 of these 9 tumors, which resulted in 2 of the MIA reclassified as agreed IA (29%). Of the 5 tumors that were completely submitted, 4 of the patients were alive with no evidence of recurrent lung cancer 7 to 9 years after excision (mean follow-up, 8.25 years). One of the 5 patients developed a metachronous primary tumor 6 years after initial tumor resection (contralateral lung, second tumor also had predominantly lepidic growth). She is currently alive and well 9 years after initial tumor resection.

IA

Observer 1 AIS/MIA 77 (26.0%) 13 (4.4%) IA 33 (11.2%) 173 (58.5%)

3.4. Radiographic comparison

NOTE. In the 3-level system (top), agreement was seen in 244 tumors (82.4%, shaded), with disagreement in 52 tumors (17.6%). When AIS and MIA grouped together as a low-risk group (bottom), agreement was seen in 250 tumors (84.5%, shaded), with disagreement in 46 tumors (15.5%). Abbreviations: AIS-adenocarcinoma in situ, MIA-minimally invasive adenocarcinoma, IA-invasive adenocarcinoma.

Radiographic size determination was performed on 91 nodules from 82 patients categorized as AIS or MIA by at least 1 pathologist. Average absolute difference between radiographic and gross size measurement was 4.1 mm (SD, 3.7 mm). Radiographic size was generally larger than gross size by an average of 2.4 mm. Of agreed AIS, 9 were GGO, and 1 was subsolid. Of agreed MIA, 17 were GGO, 21 were subsolid, and 8 were solid. For the AIS-MIA disagree, 4 were GGO, and 2 were solid. For the MIA-IA disagree, 6 were GGO, 15 were subsolid, and 6 were solid.

3.5. Survival analysis did not change the original diagnostic category. In 7 patients (20%), the additional tissue resulted in reclassification by at least 1 pathologist: 3 cases of agreed MIA were changed to agreed IA, 3 cases of disagreed IA versus MIA were changed to agreed IA, and 1 agreed AIS was changed to agreed IA. For these cases, the final tumor classification was considered the invasive category assigned after examination of all residual gross tissue.

3.3. Interobserver agreement Of 296 nodules (82.4%), 244 were classified into the same category by both observers (Table 2; simple κ = 0.63; 95% confidence interval [CI], 0.54-0.72; good agreement). Six nodules (2%) were disagreed AIS versus MIA; 45 (15%) were disagreed MIA versus IA (Fig. 1); and 1 was disagreed AIS versus IA (weighted κ = 0.67; 95% CI, 0.58-0.75; good agreement). All cases classified as AIS and MIA were nonmucinous. When AIS and MIA were grouped together as a “low risk” category, agreement between the 2 groups was seen in 84.5% of nodules (Table 2; κ = 0.65; 95% CI, 0.56-0.74; good agreement). Average absolute difference in invasion measurement was 3.4 mm (ICC, 0.80; excellent reliability), and average absolute difference in scar measurement was 2.6 mm (Supplementary Table; ICC, 0.65; good reliability). Because tumors were categorized blinded to gross tumor size, there were 8 tumors classified as agreed MIA and 1 tumor classified as agreed AIS, although the gross tumor size was greater than 3 cm. Average size of the 8 MIA was 3.9 cm

OS analysis was performed (n = 254) with mean follow-up of 5.74 years (0.03-16.87). Forty-five percent of patients were deceased at last follow-up. If a patient had more than 1 nodule, earliest diagnosis was used for nonsynchronous tumors, and largest invasive focus was used for synchronous tumors. OS was significantly different among invasive categories as determined by both observers (Fig. 2). For observer 1, 5-year OS rates were 100% for AIS, 86% for MIA, and 62% for IA (P = .0002); for observer 2, 5-year OS rates were 82% for AIS, 79% for MIA, and 63% for IA (P = .0107). Significant OS differences persisted when AIS and MIA were grouped together (Table 3). There were 37 patients with disagreement between MIA and IA, which had OS similar to patients with agreed MIA and better than agreed IA (Table 4). There was significantly higher hazard ratio (HR) for IA over AIS/MIA as determined by both observers (Table 3). However, when adjusted for other variables, the significance maintained for observer 1 only (Table 3). Separate OS analysis was performed on 190 stage I patients (Fig. 3). OS was significantly different among invasive groups for observer 1 (100% for AIS, 86.3% for MIA, 67% for IA at 5 years; P = .0010), a difference that persisted when AIS and MIA were grouped together (Table 3). However, the OS differences did not reach statistical significance for observer 2 when 3 invasive groups were considered (77.8% for AIS, 80.2% for MIA, 69.3% for IA at 5 years; P = .0827), whereas the OS difference was

Interobserver agreement in pulmonary adenocarcinoma classification

45

Fig. 1 Photomicrographs of representative cases (hematoxylin and eosin). A, Agreed AIS (original magnification ×200). Note the lepidic growth pattern along alveolar septa with no identified focus of invasion. B, Agreed MIA (×100). The tumor shows a predominately lepidic growth pattern, with a central focus of invasion measuring less than or equal to 5 mm that is associated with a scar. C, Agreed IA (×100). Lepidic growth is present at the edge, but large foci of invasive growth with papillary and acinar pattern are evident. D, Disagreed AIS versus MIA (×100). Small glands (arrows) could be interpreted as small foci of invasion, implicating MIA, or as preexisting alveoli lined by neoplastic cells with associated thickening of the alveolar walls by fibrosis, consistent with AIS. E, Disagreed MIA versus IA (×40). The largest focus of invasion was measured as 5 mm by one observer and 8 mm by the other.

significant when AIS/MIA were grouped together (P = .0404, Table 3). The difference in HR and adjusted HR were both significant for observer 1 when comparing AIS/MIA versus IA, but the difference in HR was not significant for observer 2 when adjusted for other variables (Table 3). DSS was collected for 122 patients. Ten-year DSS for AIS determined by both observers was 100%. Ten-year DSS

for MIA was 97.3% for observer 1 and 97.6% for observer 2 (2 events in MIA group for each observer). However, the DSS difference between 3 invasive groups did not achieve significance for either observer (10-year DSS for IA 80.2% for observer 1, P = .2541; 74.8% for observer 2, P = .0899) (Fig. 4). With AIS and MIA grouped together, there was a significant difference between AIS/MIA and IA for observer

46

J. M. Boland et al.

A 100

Percent survival

80

60

40

20

P < .001

AIS (n = 7) MIA (n = 60) IA (n = 187)

0 0

1

2

3

4

5

4

5

Years

B100

Percent survival

80

60

40

20

P = .011

AIS (n = 11) MIA (n = 76) IA (n = 167)

0 0

1

2

3

Years

Fig. 2 Kaplan-Meier curve of overall survival for the entire cohort (n = 254), for observer 1 (A) and observer 2 (B).

2 only (Table 3). The HR for AIS/MIA was marginally different from that observed in IA for observer 2 only, which faded when adjusted for other variables (Table 3).

4. Discussion Good agreement was present between observers in our study, with concordance in the determination of AIS, MIA, and IA in 82.4% of nodules and concordance between the combined AIS/MIA versus IA in 84.5%. When agreement was studied among 3 pathologists using a similar system, Borczuk et al [5] found moderate agreement, which is similar to what we observed. As the authors of this study pointed out, this is consistent with other assessments made by pathologists, including Clark level and Gleason grade. Thunnissen et al [21] found only fair agreement when determining invasive versus in situ/lepidic growth, based on circulating 64 representative images among 28 pathologists. The difference between the observed agreement in our study and this prior work is not surprising and likely due to the

much smaller number of observers in our study and possibly also due to the fact that all slides were reviewed in our study instead of basing invasion on a single image. Our agreement data are also likely somewhat falsely inflated because the determination was made by 2 academic pulmonary pathologists practicing at the same large-volume practice [29]. Most anxiety among pathologists seems to occur when deciding how to categorize tumors near the cutoff value between MIA and IA, as this is a logical area where disagreements will occur. There was disagreement between MIA and IA in 37 of our patients, and OS was very similar to the agreed MIA group. Therefore, it seems tumors with invasion near 5 mm are safely categorized as MIA, as expected based on the observed superior prognosis for lepidicpredominant tumors [17]. Another frequent problem is adenocarcinomas that have a central scar with invasive glands at the edge, but the center of the scar is devoid of tumor. We included the scar in invasive measurement in most cases, although explicit direction is lacking [9,10]. Whether tumor arises in preexisting scar or induces formation of the scar has been an area of historical debate [30], but most scars seem induced by invasion [2,6-8,31]. Therefore, it seems logical to include the scar in invasive measurement. Pitfalls in determination of scarring exist (tumor in a preexisting apical cap), so pathologists will still need to use judgment. One unique component of our data is the examination of gross residual tumor. Processing the entire area of gross abnormality did not change classification in 80% of cases. Thus, it seems that careful gross examination with concentration on the most suspicious areas for invasion will lead to correct classification with routine sampling in most cases. Reclassification occurred in 20% of cases, but the significance of this change in classification is debatable because small lepidic-predominant tumors also have an excellent prognosis [17]. Thus, it seems reasonable to conserve fresh tissue for research or other testing if needed, even if the tumor is classified as AIS/MIA. Proper classification of lepidic tumors greater than 3 cm with invasion less than or equal to 5 mm is largely unknown. Literature focuses on tumors less than or equal to 3 cm [3,6,7], with many studies only including tumors less than or equal to 2 cm [2,8,31]. Current practice is to classify lepidic tumors greater than 3 cm as lepidic-predominant adenocarcinoma even if invasion greater than 5 mm is not observed because literature is sparse and the entire tumor may not be practically submitted for histology [9]. We had 8 agreed MIA and 1 AIS with gross tumor size greater than 3 cm. Submission of the gross residual led to reclassification as IA in 29% of these cases, which left only 5 cases of potential AIS/MIA that were greater than 3 cm. Of these 5 cases, 4 of the patients had long-term survival (N7 years in all cases) with no recurrence of lung cancer and were all alive at last follow-up. The fifth patient had a metachronous primary tumor 6 years after the first tumor was excised and is alive and well 9 years after first diagnosis. Thus, although our data are quite limited due to the very low number of patients, it

Interobserver agreement in pulmonary adenocarcinoma classification

47

Table 3 Differences in survival and hazard ratio between AIS/MIA and invasive adenocarcinoma groups as determined by 2 observers, including the entire patient cohort (top section), stage I cohort (center section), and disease-specific survival cohort (bottom section) Observer 1

Overall survival, entire cohort (n = 254)

Total no. of cases (%) No. of events (%) Median survival, y (95% CI) Postdiagnosis survival, % (95% CI) 1y 5y 10 y P Cox proportional hazards Hazard ratio (95% CI) P Adjusted Cox proportional hazards a Hazard ratio (95% CI) P Overall survival, stage I Total no. of cases (%) cohort (n = 190) No. of events (%) Median survival, y (95% CI) Postdiagnosis survival, % (95% CI) 1y 5y 10 y P Cox proportional hazards Hazard ratio (95% CI) P Adjusted Cox proportional hazards a Hazard ratio (95% CI) P Disease-specific Total no. of cases (%) survival (n = 122) No. of events (%) Postdiagnosis survival, % (95% CI) 1y 5y 10 y P Cox proportional hazards Hazard ratio (95% CI) P Adjusted Cox proportional hazards a Hazard ratio (95% CI) P

Observer 2

AIS/MIA

IA

AIS/MIA

IA

67 (26.4) 16 (23.9) 15.5 (8.8-15.5)

187 (73.6) 99 (52.9) 7.2 (5.7-8.5)

87 (34.3) 34 (39.1) 13.0 (8.6-14.8)

167 (65.8) 81 (48.5) 7.1 (5.7-8.5)

95.5 (90.7-100) 92.5 (88.7-96.3) 87.4 (79.6-96.0) 62.2 (55.4-69.8) 66.8 (52.4-85.2) 37.8 (29.3-48.7) b.0001

92.0 (86.4-97.9) 93.9 (90.4-97.7) 79.5 (72.3-88.7) 63.1 (56.0-71.2) 60.5 (49.3-74.3) 35.8 (25.9-49.6) .0055

Reference .0002

2.76 (1.62-4.69)

Reference .0061

1.77 (1.18-2.67)

Reference .0194 60 (31.6) 13 (21.7) 15.5 (8.8-15.5)

1.94 (1.11-3.37)

Reference .4270 74 (39.0) 27 (36.5) 13.0 (8.6-15.5)

1.20 (0.77-1.86)

130 (68.4) 62 (47.7) 7.2 (6.5-9.8)

116 (61.1) 48 (41.4) 8.1 (6.5-12.5)

95.0 (89.6-100) 93.8 (89.7-98.1) 87.6 (79.3-96.7) 67.0 (59.1-76.0) 70.2 (55.1-89.3) 37.1 (26.3-52.5) .0003

93.2 (87.7-99.1) 94.8 (90.8-98.9) 79.9 (70.9-89.9) 69.3 (61.0-78.7) 60.7 (48.4-76.2) 37.0 (23.7-57.9) .0404

Reference .0006

2.86 (1.57-5.23)

Reference .0423

1.66 (1.02-2.69)

Reference .0114 44 (36.1) 2 (4.6)

2.23 (1.20-4.14)

Reference .1538 53 (43.4) 2 (3.8)

1.45 (0.87-2.40)

78 (63.9) 10 (12.8)

100 (100-100) 98.6 (95.9-100) 97.6 (93.1-100) 86.9 (78.8-95.9) 97.6 (93.1-100) 80.2 (66.7-96.6) .1082

6 (56.6) 10 (14.5)

100 (100-100) 98.4 (95.5-100) 97.9 (94.0-100) 85.5 (76.6-95.4) 97.9 (94.0-100) 74.8 (56.3-99.4) .0308

Reference .1289

3.25 (0.71-14.93) Reference .0308

4.69 (1.01-21.76)

Reference .3023

2.39 (0.46-12.48) Reference .2154

2.88 (0.54-15.37)

Abbreviations: AIS, adenocarcinoma in situ; MIA, microinvasive adenocarcinoma; IA, invasive adenocarcinoma. a Adjusted for sex, smoking status, and stage. Other variables considered in the stepwise model selection process were age, race, grade, surgery, chemotherapy, radiation, and lung cancer history.

seems that patients with well-sampled lepidic tumors greater than 3 cm that show absent or limited invasion less than 5 mm may experience the same excellent survival as patients who fulfill the current WHO criteria for AIS/MIA. However, until more data are available, it seems prudent to continue to classify these tumors as lepidic-predominant adenocarcinoma. Radiographic GGO in adenocarcinoma correlates with lepidic growth in most cases [24], but the implications of

differences between radiographic and pathologic size have not been thoroughly investigated. On average, we observed a 4-mm difference between radiologic and pathologic size, with the radiologic size tending to be larger, which has also been observed in other studies [32]. This difference could be explained by pathologic undermeasurement: lepidic tumor may be grossly unapparent, and the lung is aerated in vivo compared to pathologic specimens, which are relatively devoid of air. Although our gross sizes were measured in the

48

J. M. Boland et al.

Table 4

Overall survival for patients with discordant and concordant categorization as MIA and IA between the 2 raters

Median survival (y) Postdiagnosis overall survival 1y 5y 10 y

Discordant MIA vs IA (n = 37)

Agreed MIA (n = 48)

Agreed IA (n = 158)

13.8

13.0

7.1

89.2% (79.7-99.8) 76.8% (63.8-92.4) 58.7% (42.5-81.0)

95.8% (90.3-100) 84.6% (74.8-95.8) 53.8% (35.6-81.3)

93.6% (89.8-97.5) 61.2% (53.9-69.6) 33.7% (23.9-47.7)

Abbreviations: MIA, minimally invasive adenocarcinoma; IA, invasive adenocarcinoma.

fresh state, many pathologic studies are based on fixed size, which introduces tumor shrinkage due to formalin fixation. Radiographic overmeasurement may also occur, due to inflammation, organizing pneumonia, scarring, hemorrhage, or edema surrounding the tumor. Additional study is warranted, with consideration of tumors that have size discordance around the 3-cm cutoff and tumors that have radiologic solid component greater than or equal to 6 mm that are deemed pathologically to represent AIS/MIA. Ideally, noninvasive methods would be used to determine tumor invasiveness preoperatively. Members of our group

have been involved with development and validation of novel image analysis software, which facilitates noninvasive risk stratification based on CT imaging of pulmonary nodules [33-35]. This powerful tool shows great promise in predicting the aggressiveness of nodules, knowledge which could be used to make management decisions and optimize individualized care. Although several studies have shown 100% survival for both AIS and MIA [3,12,13], the number of AIS and MIA cases is small. If patients with AIS and MIA share the same excellent outcome, it may be possible to combine these

A 100

A 100 80

Percent survival

Percent survival

80

60

40

20

40

20

P < .001

AIS (n = 5) MIA (n = 55) IA (n = 130)

0 0

1

2

3

4

P = .25

AIS (n = 5) MIA (n = 39) IA (n = 78)

0

5

0

Years

B 100

1

2

3

4

5

4

5

Years

B 100

80

80

Percent survival

Percent survival

60

60

40

20

60

40

20

P = .083

AIS (n = 9) MIA (n = 65) IA (n = 116)

0 0

1

2

3

4

5

Years

Fig. 3 Kaplan-Meier curve of overall survival for patients in stage I cohort (n = 190), observer 1 (A) and observer 2 (B).

P = .090

AIS (n = 8) MIA (n = 4 5) IA (n = 69)

0 0

1

2

3

Years

Fig. 4 Kaplan-Meier curve of lung cancer-specific survival for stage I patients (n = 122), observer 1 (A) and observer 2 (B).

Interobserver agreement in pulmonary adenocarcinoma classification categories in the future, which would increase agreement between observers. However, if there is a difference in outcome, it would support keeping these categories as separate entities. Our results indicate that although the differences in OS predicted by this classification are significant when determined by different observers, interobserver variability is evident, which is logical when considering the inherent subjectivity in measurement. We observed intermediate OS for MIA, between AIS and IA, which was true for both observers. This is in contrast to studies with a small number of AIS/MIA cases that have reported 100% OS [24,28], but many of these studies were performed on East Asian patients, which have different demographic and genetic features than tumors arising in Western patient populations. This difference is largely diminished when DSS is considered, where AIS and MIA both have an excellent survival, and therefore, it might be other factors (age, smoking status, comorbidities, multifocality, and genetics) that lead to the worse OS for the MIA group. Our DSS analysis is limited by the relatively low number of AIS/MIA cases. However, DSS was 100% at 10 years for AIS determined by both observers. DSS for MIA at 10 years was 97.3% and 97.6% for each observer, which is excellent, but there were rare lung cancer events that occurred in patients classified as MIA. This would indicate that rare patients with MIA will experience progression from lung cancer but at a rate much lower than patients with IA. However, this could not be confirmed because the difference in DSS observed in IA (74.8% and 80.2%) did not reach significance compared to AIS/MIA. We do not feel that this implies that there is no difference in DSS between AIS/MIA and IA at large. Instead, because our cohort was enriched for tumors with a lepidic component, this likely reflects the fact that our selected cohort has a superior prognosis compared to nonselected pulmonary IA, and thus, the difference in DSS between our selected IA group and the AIS/MIA group is diminished, compounded by the low number of AIS/MIA cases. The excellent DSS for patients with AIS and MIA raises interesting questions about overtreatment, as many would argue that less aggressive therapies (sublobar resection, observation, no treatment) are valid considerations for these indolent lesions. Prospective studies will help clarify this issue. In summary, good agreement was present between observers when classifying tumors as AIS, MIA, and IA, which may reflect our large-volume practice and subspecialization. However, differences in observed OS were present between observers, reflecting interobserver variability. Tumors with disagreement between MIA and IA had survival similar to agreed MIA, and thus, borderline cases can be confidently classified as MIA. Significant differences in OS were present between invasive groups for both observers. Patients with AIS and MIA experienced excellent DSS, although the significance of this improved DSS compared to IA could not be definitively established.

49

Supplementary data Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.humpath.2015.12.010.

References [1] Liebow AA. Bronchiolo-alveolar carcinoma. Adv Intern Med 1960; 10:329-58. [2] Noguchi M, Morikawa A, Kawasaki M, et al. Small adenocarcinoma of the lung. Histologic characteristics and prognosis. Cancer 1995;75: 2844-52. [3] Suzuki K, Yokose T, Yoshida J, et al. Prognostic significance of the size of central fibrosis in peripheral adenocarcinoma of the lung. Ann Thorac Surg 2000;69:893-7. [4] Terasaki H, Niki T, Matsuno Y, et al. Lung adenocarcinoma with mixed bronchioloalveolar and invasive components: clinicopathological features, subclassification by extent of invasive foci, and immunohistochemical characterization. Am J Surg Pathol 2003;27: 937-51. [5] Borczuk AC, Qian F, Kazeros A, et al. Invasive size is an independent predictor of survival in pulmonary adenocarcinoma. Am J Surg Pathol 2009;33:462-9. [6] Shimosato Y, Suzuki A, Hashimoto T, et al. Prognostic implications of fibrotic focus (scar) in small peripheral lung cancers. Am J Surg Pathol 1980;4:365-73. [7] Maeshima AM, Niki T, Maeshima A, Yamada T, Kondo H, Matsuno Y. Modified scar grade: a prognostic indicator in small peripheral lung adenocarcinoma. Cancer 2002;95:2546-54. [8] Sakurai H, Maeshima A, Watanabe S, et al. Grade of stromal invasion in small adenocarcinoma of the lung: histopathological minimal invasion and prognosis. Am J Surg Pathol 2004;28:198-206. [9] Travis WD, Brambilla E, Noguchi M, et al. International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society international multidisciplinary classification of lung adenocarcinoma. J Thorac Oncol 2011;6:244-85. [10] Travis WD, Brambilla E, Burke AP, Marx A, Nicholson AG. WHO classification of tumours of the lung, pleura, thymus and heart. In: Bosman FT, Jaffe ES, Lakhani SR, Ohgaki H, editors. World Health Organization Classification of Tumors. Lyon: IARC Press; 2015. [11] Sica G, Yoshizawa A, Sima CS, et al. A grading system of lung adenocarcinomas based on histologic pattern is predictive of disease recurrence in stage I tumors. Am J Surg Pathol 2010;34:1155-62. [12] Yoshizawa A, Motoi N, Riely GJ, et al. Impact of proposed IASLC/ ATS/ERS classification of lung adenocarcinoma: prognostic subgroups and implications for further revision of staging based on analysis of 514 stage I cases. Mod Pathol 2011;24:653-64. [13] Russell PA, Wainer Z, Wright GM, Daniels M, Conron M, Williams RA. Does lung adenocarcinoma subtype predict patient survival?: a clinicopathologic study based on the new International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society international multidisciplinary lung adenocarcinoma classification. J Thorac Oncol 2011;6:1496-504. [14] Hung JJ, Jeng WJ, Chou TY, et al. Prognostic value of the new International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society lung adenocarcinoma classification on death and recurrence in completely resected stage I lung adenocarcinoma. Ann Surg 2013;258:1079-86. [15] Yanagawa N, Shiono S, Abiko M, Ogata SY, Sato T, Tamura G. New IASLC/ATS/ERS classification and invasive tumor size are predictive of disease recurrence in stage I lung adenocarcinoma. J Thorac Oncol 2013;8:612-8.

50 [16] Hung JJ, Yeh YC, Jeng WJ, et al. Predictive value of the International Association for the Study of Lung Cancer/American Thoracic Society/ European Respiratory Society classification of lung adenocarcinoma in tumor recurrence and patient survival. J Clin Oncol 2014;32:2357-64. [17] Kadota K, Villena-Vargas J, Yoshizawa A, et al. Prognostic significance of adenocarcinoma in situ, minimally invasive adenocarcinoma, and nonmucinous lepidic predominant invasive adenocarcinoma of the lung in patients with stage I disease. Am J Surg Pathol 2014;38:448-60. [18] Warth A, Cortis J, Fink L, et al. Training increases concordance in classifying pulmonary adenocarcinomas according to the novel IASLC/ATS/ERS classification. Virchows Arch 2012;461:185-93. [19] Warth A, Muley T, Meister M, et al. The novel histologic International Association for the Study of Lung Cancer/American Thoracic Society/ European Respiratory Society classification system of lung adenocarcinoma is a stage-independent predictor of survival. J Clin Oncol 2012; 30:1438-46. [20] Aberle DR, Adams AM, Berg CD, et al. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med 2011;365:395-409. [21] Thunnissen E, Beasley MB, Borczuk AC, et al. Reproducibility of histopathological subtypes and invasion in pulmonary adenocarcinoma. An international interobserver study. Mod Pathol 2012;25:1574-83. [22] Warth A, Stenzinger A, von Brunneck AC, et al. Interobserver variability in the application of the novel IASLC/ATS/ERS classification for pulmonary adenocarcinomas. Eur Respir J 2012;40:1221-7. [23] Grilley-Olson JE, Hayes DN, Moore DT, et al. Validation of interobserver agreement in lung cancer assessment: hematoxylineosin diagnostic reproducibility for non-small cell lung cancer: the 2004 World Health Organization classification and therapeutically relevant subsets. Arch Pathol Lab Med 2013;137:32-40. [24] Takahashi M, Shigematsu Y, Ohta M, Tokumasu H, Matsukura T, Hirai T. Tumor invasiveness as defined by the newly proposed IASLC/ ATS/ERS classification has prognostic significance for pathologic stage IA lung adenocarcinoma and can be predicted by radiologic parameters. J Thorac Cardiovasc Surg 2014;147:54-9. [25] Yoshizawa A, Sumiyoshi S, Sonobe M, et al. Validation of the IASLC/ ATS/ERS lung adenocarcinoma classification for prognosis and

J. M. Boland et al.

[26]

[27]

[28]

[29]

[30] [31]

[32]

[33]

[34]

[35]

association with EGFR and KRAS gene mutations: analysis of 440 Japanese patients. J Thorac Oncol 2013;8:52-61. Russell PA, Barnett SA, Walkiewicz M, et al. Correlation of mutation status and survival with predominant histologic subtype according to the new IASLC/ATS/ERS lung adenocarcinoma classification in stage III (N2) patients. J Thorac Oncol 2013;8:461-8. Mansuet-Lupo A, Bobbio A, Blons H, et al. The new histologic classification of lung primary adenocarcinoma subtypes is a reliable prognostic marker and identifies tumors with different mutation status: the experience of a French cohort. Chest 2014; 146:633-43. Gu J, Lu C, Guo J, et al. Prognostic significance of the IASLC/ATS/ ERS classification in Chinese patients—a single institution retrospective study of 292 lung adenocarcinoma. J Surg Oncol 2013;107: 474-80. Noguchi M, Minami Y, Iijima T, Matsuno Y. Reproducibility of the diagnosis of small adenocarcinoma of the lung and usefulness of an educational program for the diagnostic criteria. Pathol Int 2005;55: 8-13. Yokoo H, Suckow EE. Peripheral lung cancers arising in scars. Cancer 1961;14:1205-15. Kurokawa T, Matsuno Y, Noguchi M, Mizuno S, Shimosato Y. Surgically curable “early” adenocarcinoma in the periphery of the lung. Am J Surg Pathol 1994;18:431-8. Lampen-Sachar K, Zhao B, Zheng J, et al. Correlation between tumor measurement on computed tomography and resected specimen size in lung adenocarcinomas. Lung Cancer 2012;75:332-5. Maldonado F, Boland JM, Raghunath S, et al. Noninvasive characterization of the histopathologic features of pulmonary nodules of the lung adenocarcinoma spectrum using computer-aided nodule assessment and risk yield (CANARY)—a pilot study. J Thorac Oncol 2013;8:452-60. Maldonado F, Duan F, Raghunath SM, et al. Noninvasive CT-based risk stratification of lung adenocarcinomas in the national lung screening trial. Am J Respir Crit Care Med 2015;192:737-44. Raghunath S, Maldonado F, Rajagopalan S, et al. Noninvasive risk stratification of lung adenocarcinoma using quantitative computed tomography. J Thorac Oncol 2014;9:1698-703.