[Breast carcinoma with predominant neuroendocrine differentiation].

Neuroendocrine differentiation can be identified in a subset of human breast carcinomas, either as scattered cells or as a predominant neuroendocrine component. We report a case of an invasive breast carcinoma largely composed of neuroendocrine cells. Eight years after a left mammary lumpectomy for a pT2N1MO SBR III invasive ductal carcinoma, a 67-years-old woman presented with a metastastic neuroendocrine sternal mass. To establish a relationship between mammary carcinoma and bone metastasis, histological slides of both the breast tumor and axillary lymph nodes were reviewed, and an immunohistochemical study was performed. They showed that: a) the mammary carcinoma was composed of a majority of small and large neuroendocrine cells synaptophysin +, NCAM+, chromogranin - (80%), associated with 2 other differentiated non endocrine components, one of metaplastic squamous carcinoma (10%) and the other of ductal carcinoma (10%); b) 4 axillary lymph nodes were involved by the ductal component which contained few NCAM + but synaptophysin - cells; c) Estrogen and progesterone receptors and HER2 were negative in the breast tumor and the metastatic nodes. We discuss the histogenesis of composite mammary carcinomas with neuroendocrine differentiation, the outcome of each component and the prognostic relevance of such a diagnosis.