[So-called "carcinoid tumor of the breast"--a case report].

A 70-year-old woman underwent modified radical mastectomy following excisional biopsy of a right breast mass. The excised tumor was 1.4 cm in diameter. The mastectomy specimen and lymph nodes were negative for malignancy. Histologically, the tumor cells were mainly oval and had formed solid nests in the thick fibrous stroma. The cytoplasm was fine granular and contained many argyrophilic granules. The argentaffin reaction was negative. Electron microscopy revealed oval-shaped light cells and stellate-shaped dark cells. Both types of tumor cells contained abundant filaments, well-developed rough surfaced endoplasmic reticulum and many neurosecretory-type granules measuring 190 approximately 360 nm in diameter. Intracytoplasmic lumina were not discerned. The relationship between carcinoid and conventional breast carcinoma was discussed.