Minimally invasive adenocarcinomas of the lung.

Current World Health Organization (WHO) classification of lung adenocarcinomas includes noninvasive bronchioloalveolar carcinoma (BAC) and several patterns of invasive adenocarcinoma. The most common is a mixed subtype of adenocarcinoma. This group is very heterogenous and includes a wide spectrum of tumors ranging from adenocarcinomas with a dominant BAC growth pattern (lepidic growth) to frankly invasive adenocarcinoma with no BAC component. There is a tendency among clinicians to regard tumor as BAC if any significant amount of lepidic growth pattern within the tumor is identified. The change in WHO definition of BAC and introduction of mixed subtype of adenocarcinoma resulted in disconnect between surgical pathologists and clinicians regarding the use of terminology and criteria for diagnosis of BAC and mixed subtype of adenocarcinoma. It is clear that pure BAC is an extremely rare tumor, whereas mixed subtypes of adenocarcinomas may have various clinical presentations and outcomes. The mounting evidence suggests that a subset of mixed subtype of adenocarcinomas with areas of BAC and focal invasion probably represent more indolent tumors. On the basis of the published data, there is a proposal to define a subcategory of "minimally invasive adenocarcinoma" of the lung. Many morphologic factors seem to play a role in predicting the behavior of these tumors. Depending on the results of ongoing clinical trials, surgical management of these tumors may change in a near future.