Adenoma of type 2 pneumocytes with oncocytic features.

An adenoma of type 2 pneumocytes in the periphery of the left lung was an incidental finding at the autopsy of a 28-year-old woman. Light microscopy revealed a predominantly papillary growth with oncocytic features. Ultrastructurally, multilaminated bodies and many mitochondria were found in the tumor cells and tubular myelin in the extracellular spaces. Immunohistochemistry revealed surfactant apoprotein in tumor cells and extracellularly.