Lung tumors of uncertain histogenesis.

Unusual lung tumors of uncertain origin have been described briefly concerning benign clear cell (sugar) tumor and, in more detail, concerning pneumocytoma (so-called sclerosing hemangioma). Melanocytic differentiation of clear cell tumor, which is peculiar to the lung, has been suggested recently. Sclerosing hemangioma, also unique to the lung, is now considered to be a tumor (neoplasm) related to alveolar epithelial cells. It shows invasive growth and multiplicity (or aerogenous metastasis), but is very rarely capable of lymph node metastasis. It should be designated as pneumocytoma.