Adenocarcinoma in situ , Minimally Invasive Adenocarcinoma, and Invasive Pulmonary Adenocarcinoma- Analysis of Interobserver Agreement, Survival, Radiographic Characteristics and Gross Pathology in 296 nodules

Summary The IASLC/ATS/ERS and 2015 WHO classifications of lung adenocarcinoma recommend designating tumors showing entirely lepidic growth as adenocarcinoma in situ (AIS), and lepidic tumors with invasion ≤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 is limited, and further validation of the superior survival of AIS and MIA is needed. 296 surgically excised pulmonary adenocarcinomas were reviewed from 254 patients (1997-2009). Slides were independently reviewed by two pulmonary pathologists who categorized tumors as AIS, MIA, or IA. 244 of 296 nodules (82.4%) were agreed upon by both observers: 10 AIS, 61 MIA and 173 IA (kappa = 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 (DSS) was 100% for AIS (both observers), 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.