Pulmonary adenocarcinoma: the expanding spectrum of histologic variants.

Pulmonary adenocarcinoma is one of the most common types of lung cancer. Traditionally, adenocarcinomas have been divided based on their degree of resemblance to their parent tissues into 3 histopathologic types: well, moderately, and poorly differentiated. In the majority of cases, this schema is sufficient to categorize these lung tumors. However, there is a considerable group of tumors in which the histology is not that of the classic gland-forming neoplasm. Thus, although the terminology of adenocarcinoma is applied in such cases, the histopathologic features are different from those of the more conventional variants. The current review addresses these unusual variants and the importance of recognizing and properly categorizing them to avoid unnecessary additional workup or possible misdiagnosis.