Small cell (oat cell) carcinoma of the breast.

A case of small cell (oat cell) carcinoma, which represents both the most distinctive and the least common type of breast carcinoma with neuroendocrine differentiation and usually shows the most aggressive behavior, is described. Radical mastectomy was performed on a 56-year-old female for a 10 cm tumor located in the outer part of the right breast with cutaneous ulceration Microscopically, the tumor predominantly consisted of a diffuse proliferation of small, round to ovoid cells with hyperchromatic nuclei and ill-defined, scant cytoplasm that was reminiscent of oat cell carcinoma of the lung. There were foci of invasive ductal carcinoma and ductal carcinoma in situ. Small cell carcinoma areas constituted approximately 90% of the neoplasm. The patient had axillary lymph node metastasis. The small tumor cells were argyrophilic and positive for CAM5.2, carcinoembryonic antigen, neuron-specific enolase, Leu-7, chromogranin A and synaptophysin. Flow cytometric analysis showed an aneuploid DNA content. The patient was alive and well without disease 4 years after surgery. Small cell carcinomas of the breast may exhibit a spectrum of malignancy that is comparable to similar tumors at better known primary sites.