Diagnostic cytological features of neuroendocrine differentiated carcinoma of the breast.

Neuroendocrine (NE) features characterize a minority of carcinomas of the breast corresponding to definite subtypes, which cover a wide spectrum of differentiation. Breast metastases from NE tumours of gastrointestinal origin are not rare, and to determine whether NE carcinomas in the breast could be differentiated from other tumours on fine needle aspiration (FNA) we analysed the cytological features of 13 primary NE breast carcinomas of different types (7 carcinoid-like, 5 mucinous and 1 solid spindle cell). Smears of carcinoid-like carcinomas showed specific features that made it possible to differentiate them from other primary tumours, but not from breast metastases of NE carcinomas. These features were: cell clusters with rigid borders, single cells with a plasmacytoid appearance and peripheral cytoplasmic granules evident on Giemsa staining and immunoreactive for chromogranin A. In mucinous NE carcinomas such granules were less apparent, and the cytological features could have been mistaken for those of fibroadenomas, as in the case of non-NE mucinous carcinomas. The solid spindle cell type showed noncohesive fusiform cells and moderate nuclear pleomorphism, a pattern similar to that of atypical carcinoids of the lung.