It’s not uncommon for a question here to be about the a pathologist’s terminology on a report that equivocates about whether a lesion is bronchioloalveolar carcinoma (BAC) or another form of adenocarcinoma, perhaps “well-differentiated adenocarcinoma”, especially if it has a radiographic appearance of a hazy infiltrate or many small ground glass opacities. Meanwhile, there’s a new classification of lung cancer subtypes that obliterates the term BAC, instead favoring a definition of adenocarcinoma in situ, classifying small non-invasive lesions previously called BAC as a pre-malignant condition. How have the changes over the past few years changed how we should approach BAC?
I would have to say that the new reassignment of BAC as adenocarcinoma in situ hasn’t taken the lung cancer world by storm and that I still think of the clinical entity as BAC. For the preceding decade, the definition the pathologist’s used technically excluded a lesion with even 1% or 5% of the lesion being invasive as being called BAC, even if it acted for all the world like BAC. Clinicians learned not to be too hung up on a pathologist’s technical definitions and tended to define BAC more functionally/operationally. General oncologists and expert lung cancer specialists alike managed BAC based on the overall picture of how it behaved if it looked like a BAC pattern.






