The International association for the study of cancer (IASLC)/American thoracic society (ATS)/European respiratory society (ERS) has established a new subclassification of lung adenocarcinoma, especially for the lepidic pattern component, formerly called bronchioloalveolar adenocarcinoma (BAC). According to the new classification, BAC has been classified into the following 4 main subtypes: adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), invasive adenocarcinoma (IA), and variants of invasive adenocarcinoma (VIA). An observational study was conducted to validate this classification in patients with pathological stage IA pulmonary adenocarcinoma.