Composite type of breast carcinoma with endocrine differentiation: a cytological and immunohistochemical study.

We describe a case of breast carcinoma with endocrine differentiation containing a mixture of three different histological features that occurred in a 71-year-old woman. Histologically, the tumor was predominantly intraductal, but slightly invasive. In the intraductal lesion, the tumor consisted mainly of ovoid to round cells with a modest to abundant amount of granular eosinophilic cytoplasm or intracytoplasmic mucin (mucin-producing carcinoma in situ). It also consisted, in part, of plump spindle cells with scant cytoplasm that contained argyrophilic granules in a trabecular pattern or an arrangement of perivascular pseudorosettes (atypical carcinoid tumor like-features). Mucous lake and tumor cells floating in mucin were seen in the invasive lesion (mucinous carcinoma). Immunohistochemical staining revealed endocrine differentiation of the tumor cells of both intraductal and invasive lesions. These findings suggest that the different histological features derived from pluripotent cells upon endocrine differentiation, and that endocrine differentiation of the tumor cells had already occurred at an earlier stage of carcinogenesis, prior to the appearance of the mucinous carcinoma. Cytologically, plasmacytoid tumor cells appeared in loosely cohesive clusters or as sparsely single cells in a background of a mucinous substance.