Lung Adenocarcinoma Staging Using the 2011 IASLC/ATS/ERS Classification: A Pooled Analysis of Adenocarcinoma In Situ and Minimally Invasive Adenocarcinoma.

BACKGROUND: Lung adenocarcinoma accounts for almost 60% of non-small-cell lung cancer. According to the 2011 International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS) classification and 2015 World Health Organization classification of tumors of the lung, lepidic-predominant adenocarcinomas ≤ 3 cm in size can be classified as adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), and invasive adenocarcinoma, lepidic predominant. AIS lesions, which are noninvasive, and MIA lesions, which show ≤ 0.5 cm of invasion, have been recommended to be considered stage pTis (adenocarcinoma) and pT1(mi), respectively. We conducted a systematic analysis of the published data to evaluate the prognostic differences between AIS and MIA.

MATERIALS AND METHODS: A comprehensive search of published studies was conducted from the electronic databases using relevant search criteria. Studies that reported outcomes for ≥ 8 cases classified as AIS or MIA using the 2011 IASLC/ATS/ERS criteria were selected for the present analysis. A systematic analysis of the extracted data were performed using Comprehensive Meta-Analysis software, version 2.2.

RESULTS: Nineteen studies published from 2011 to 2015 were eligible. A total of 972 patients were included (429 with AIS and 294 with MIA; 2 studies reported AIS and MIA together, n = 249). The median age was 65.5 years, 63% were female, and 40% were smokers. The 5-year disease-free survival rate for the whole population was 97.9%. The 5-year disease-free survival rate was 100% for AIS and MIA pooled from the studies that reported the 2 groups separately. The 5-year overall survival rate for the entire group was 97.5%, and the 5-year overall survival rate was 100% for AIS and 98.5% for MIA.

CONCLUSION: No significant differences were found in the survival rates between patients with lung adenocarcinoma categorized as MIA or AIS. This finding raises questions regarding the evidence for TNM staging of AIS and MIA as recommended by the 2011 IASLC/ATS/ERS and 2015 World Health Organization classification of tumors of the lung and should be reevaluated with further studies.