Reclassification of early stage pulmonary adenocarcinoma and its consequences

The classification of pulmonary adenocarcinoma has recently undergone several proposed changes. Among these, the most striking pertains to the discontinuation of the term "bronchioloalveolar carcinoma (BAC)" and its replacement by the terms "adenocarcinoma in situ (AIS)" or "minimally invasive adenocarcinoma (MIA)" for small solitary adenocarcinomas with either pure bronchiolalveolar growth or predominant bronchioloalveolar growth and ≤5 mm invasion, respectively, in resection specimens. The recommendation for these new concepts was based on discussion and review of the literature by a panel of experts from multiple disciplines. However, the results of a recent study investigating the topic of early stage adenocarcinoma (pT1N0M0) which was based on an actual series of cases, have raised questions as to the concept, validity and justification of such new terminology and have reinforced the need to evaluate actual cases that meet the newly proposed definitions and compare them in terms of patient outcome. This is even more important when proposing terminology that implies benign behavior and that could result in a false sense of security putting patients at risk for suboptimal treatment approaches. The controversies surrounding these issues are the subject of this work.