Well-differentiated adenocarcinoma - Bronchioloalveolar carcinoma - In situ adenocarcinoma: A conundrum

Over the last decade, considerable changes have been made to the classification of pulmonary adenocarcinoma, mainly with respect to the classification of small solitary tumors. The main goal seems to have been the identification of tumors that not only follow an indolent clinical course but that can also be treated more conservatively. Thus, the most important change to the classification of lung adenocarcinoma was proposed for a tumor no greater than 3.0 cm in size with a pure lepidic growth pattern and lacking stromal, vascular, or pleural invasion, which should now be categorized as in situ adenocarcinoma. At the same time, a category of minimally invasive adenocarcinoma was proposed for tumors with a predominantly lepidic growth pattern, <3 cm in size, and with <5 mm invasion in greatest dimension in any 1 focus. What is interesting about all these developments is the fact that all the publications on this issue have been presented under the terms of small adenocarcinomas or bronchioloalveolar carcinoma. Unfortunately, the literature reviews that have proposed the change in nomenclature to in situ adenocarcinoma have not offered a more in-depth assessment of these neoplasms. More recently, a publication of a large series of cases of small adenocarcinomas has offered a different view and underscored some of the important issues that need to be taken into account before a serious change in the nomenclature can be considered.