Papillary pneumocytoma of the lung. An immunohistochemical and electron microscopic study.

Papillary pneumocytoma, so-called sclerosing hemangioma of the lung, is a benign pulmonary neoplasm. In the present study, clinical aspects, immunohistochemical characteristics, and ultrastructural findings of two cases of such tumors are described. Using a panel of various antibodies, the authors found that cytokeratin, Leu-M1 and Ber-EP4 were expressed only in papillary areas. Similarly, apocrine epithelial antigen was positive in cells lining papillary stalks. In contrast, epithelial membrane antigen (EMA) stained cells both in solid and papillary areas. CD 31, Ulex 1 and factor VIII-related antigen were positive only in stromal vessels, as desmin and muscle actin. Vimentin was positive in stromal cells and in papillary areas in one case. KP 1 staining was negative in neoplastic cells. Ultrastructurally, both neoplastic cell types showed features of epithelial cells, and the cells lining papillary stalks contained lamellar bodies characteristic to type II pneumocytes. The evidence obtained clearly shows that the neoplastic cells of this tumor are of epithelial type; one cell type represents neoplastic type II pneumocytes, and another cell type represents the heterogeneous group of epithelial cells, also sharing features of type I pneumocytes.