Myoblastomatoid (histiocytoid) carcinoma of the breast. A type of apocrine carcinoma.

Thirteen carcinomas of the breast having in common neoplastic cells with granular to foamy cytoplasm are described. These cells exhibit apocrine differentiation as demonstrated by immunocytochemical and in situ hybridization studies. These tumors can be easily misinterpreted as either fibrohistiocytic or myoblastomatoid (granular cell) tumors. Therefore, the designation of myoblastomatoid (histiocytoid) invasive carcinomas seems the most appropriate for this specific group of apocrine carcinomas.