Pros: the present classification of mucinous adenocarcinomas of the lung

Mucinous lung adenocarcinomas are relatively uncommon and represent 2% to 10% of all lung adenocarcinomas. The 2015 WHO classification of lung tumors essentially adopted the International Association for the Study of Lung Cancer proposal for the reclassification of lung adenocarcinomas (1,2). A proposal to reclassify mucinous bronchioloalveolar adenocarcinoma to invasive mucinous adenocarcinoma was based on the observation that majority, if not all, of formerly known mucinous bronchioloalveolar adenocarcinomas are invasive and show more aggressive behavior when compared to non-mucinous bronchioloalveolar adenocarcinoma (3). All mucinous adenocarcinomas are currently classified under variants of lung adenocarcinoma and in addition to invasive mucinous adenocarcinoma also include colloid adenocarcinoma, and enteric adenocarcinoma. The classification into separate variants is based on morphology, immunoprofile, genomic and clinical characteristics. An alternative approach to lung adenocarcinoma, classifies mucinous adenocarcinomas as the non-terminal respiratory unit (TRU)-type because of their origin from the bronchial epithelium or submucosal glands and a gastric-mucin phenotype (4).