Oncocytic mucoepidermoid tumor of the bronchus

Mucoepidermoid neoplasms of the bronchus are uncommon tumors believed to arise from bronchial mucus glands. Reported ultrastructural evaluation has been limited to two cases in a single publication. The authors report the light microscopic and ultrastructural features of a third case with similar findings. An unusual finding not previously reported was the presence of numerous typical onocytes shown by light and electron microscopy. Morphologic forms intermediate between the mucus cells, epidermoid cells, and oncocytes were identified ultrastructurally. The origin of onocytes has been of some controversy. The presence of these cells associated with a mucoepidermoid tumor of the bronchus suggests a common progenitor cell. The transitional forms identified ultrastructurally support the notion that oncocytes are the result of a metaplastic process.