A breast carcinoid tumor with special reference to ultrastructural study.

A case of a carcinoid tumor of the left breast of an 83-year-old male is reported. On light microscopy the tumor showed the classical pattern of a carcinoid tumor. Neurosecretory granules were verified ultrastructurally, membrane-bound, about 180 nm in diameter, and possessing electron-dense contents. Some tumor cells had long slender cytoprocesses with small clear round granules other than neurosecretory ones.