Fine needle aspiration of mammary carcinoma with features of a carcinoid tumor. A case report with immunohistochemical and ultrastructural studies.

We report a case of fine needle aspiration (FNA) of a mammary carcinoma with features of a carcinoid tumor from the right breast of an 87-year-old woman who had a history of a left mammary "carcinoid" tumor diagnosed histologically three years earlier. Aspiration cytology revealed extremely rich cellularity. The neoplastic cells were mostly dispersed; however, they also could be found in loose clusters, acinus-like formations and occasionally in small sheets. They were relatively small and regular and contained fairly uniform, mostly round and oval nuclei with moderately abundant cytoplasm. Many of the tumor cells had eccentric nuclei. Immunohistochemical study revealed that tumor cells from both the cytologic smear and histologic section were reactive with antibody against serotonin. Ultrastructural study performed on the simple right mastectomy specimen showed many membrane-bound, dense-core particles in the cytoplasm of neoplastic cells, consistent with neuroendocrine secretory granules.