<prompt> Which of the following is NOT true about Bronchoalveolar carcinoma?AdenocarcinomaStromal invasion with desmoplasiaPreservation of Alveolar structureGrows along pre-existing anatomical structures  <response>: Ans. b Stromal invasion with desmoplasia Ref. Robbins 7th76lBy definition, bronchioalveolar ca do not demonstrate destruction of alveolar architecture or stromal invasion with desmoplasia, features that would merit their classification as frank adenocarcinomas.BRONCHIOLOALVEOLAR CARCINOMAS BACS Included as a subtype of adenocarcinomas in the current WHO classification of lung tumors. Involve peripheral parts of the lung, either as a single nodule or, more often, as multiple diffuse nodules that may coalesce to produce pneumonia-like consolidation. The key feature of BACs is their growth along preexisting structures and preservation of alveolar architecture. The tumor cells grow in a monolayer on top of the alveolar septa, which serves as a scaffold this has been termed a lepidic growth pattern, an allusion to the neoplastic cells resembling butterflies sitting on a fence. The two subtypes of BACs are:- Mucinous comprising tall, columnar cells with prominent cytoplasmic and intra-alveolar mucin and- Non-mucinous The cell of origin for peripheral adenocarcinomas have now identified a population of multipotent cells at the bronchioalveolar duct junction, termed bronchioalveolar stem cells BASCs. 