Alveolar cell carcinoma: Does it exist?

A pulmonary tumor with a light microscopic appearance typical of bronchiolar-alveolar cell carcinoma was studied with the electron microscope. The tumor was composed of cells which were remarkably similar to Type 11 alveolar lining cells (granular pneumocytes). Some investigators doubt the existence of alveolar cell carcinoma as a distinct entity, and advocate lumping together all such tumors with pulmonary adenocarcinomas. Evidence presented here and elsewhere, however, indicates that some bronchiolar-alveolar cell carcinomas are composed of cells with the ultrastructural characteristics of granular pneumocytes. Classification of these neoplasms should take electron microscopic findings into account, since ultrastructural differences between tumors with similar light microscopic appearances may eventually be correlated with varying patterns of clinical disease.