Pancreatic Neuroendocrine Carcinoma Metastatic to the Breast as Part of the Multiple Endocrine Neoplasia Type 1 Syndrome.

Breast metastases from nonmammary tumors are rare. We report here the first case of pancreatic neuroendocrine carcinoma metastatic to the breast in a patient with possible multiple endocrine neoplasia type 1. The diagnosis was supported by histological examination, immunohistochemistry, and ultrastructural analysis. This observation emphasizes the importance of clinical data for an accurate diagnosis, especially during intraoperative examination. When pathologists are faced with an unusual breast tumor larger than 2 cm, we would recommend freezing and/or saving pieces of tissue for ultrastructural analysis, which might help in the diagnosis.