Bronchioloalveolar carcinoma (BAC) has been recognized as a type, albeit unusual, of non-small cell lung cancer (NSCLC) since 1876.However, that disease now refers only to peripheral lung adenocarcinomas characterized by a lepidic pattern of growth.This encompasses a spectrum of tumors, including in situ adenocarcinomas, as well as those which are minimally invasive and invasive.Moreover, there are two different cytological subtypes: non-mucinous and mucinous.