Histiocytoid carcinoma of the male breast.

Histiocytoid carcinoma of the breast is a rare tumor with approximately 30 cases reported, all occurring in female patients. We report the first case of histiocytoid breast carcinoma in a male patient. A 68-year-old man presented with a 2.5-cm breast mass. Microscopic examination of the needle core biopsy revealed a diffuse (lobular type) infiltration of tumor cells as angulated clusters, linear arrangements, small nests, and individual cells; there was no duct formation. The nuclei were round-oval and hyperchromatic with inconspicuous nucleoli and finely dispersed chromatin. The cytoplasm was abundant, was amphophilic, and ranged from granular to vacuolated. A subset of tumor cells contained periodic acid Schiff-positive cytoplasmic material, which was largely but incompletely removed by diastase treatment. There was minimal nuclear pleomorphism, and mitotic figures were inconspicuous. The intervening stroma was densely fibrotic, and the tumor infiltrated among tightly packed collagen bundles. Immunohistochemistry was positive for estrogen receptor, progesterone receptor, androgen receptor, vimentin, epithelial membrane antigen, and pan-cytokeratin. The tumor was negative for CK7, CAM5.2, 34BE12, AE1/AE3, GCDFP-15 (BRST-2), E-cadherin, and CD68. The mastectomy resection demonstrated similar histologic findings. Sentinel lymph node biopsy was negative. The morphology of this tumor is similar to that described for histiocytoid carcinoma of the female breast, a rare entity. Such tumors are felt to be variants of lobular carcinomas, which is supported by diffuse infiltrative growth, loss of E-cadherin expression, and strong ER positivity. We believe our case to be the first reported example of histiocytoid carcinoma in a male breast.