Bronchoalveolar carcinoma (BAC) is a variant of non-small cell lung cancer (NSCLC) that, in recent years, has received a new identity and nomenclature from the histology perspective. The orphan among lung cancers has found a family, albeit with some newfound stepbrothers and sisters. The overhaul in the classification system of solitary adenocarcinomas has been driven by the purpose of identifying tumors that have an indolent clinical course and can be treated with a more conservative approach and a higher success rate. BAC is now consisting of five types based on histology: adenocarcinoma in situ, minimally invasive adenocarcinoma, lepidic predominant nonmucinous adenocarcinoma, invasive mucinous adenocarcinoma, and invasive adenocarcinoma with its subtypes.
Until the previous decade, strict pathologic criteria defined BAC as a tumor arising from terminal bronchiolar and alveolar acinar epithelia with an absence of invasion through the alveolar basement membrane into the pulmonary parenchyma. A growing consensus has been to subclassify adenocarcinoma with radiologic features of ground-glass opacities, with no or minimal extrathoracic spread, and histology demonstrating a lepidic growth pattern in the presence or absence of associated minimally invasive or invasive disease. These types of lung cancers are seen more often in younger patients who are typically non-smokers and with an almost equal 1:1 gender predisposition, or with a slight female predominance.
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