[Neuroendocrine tumor of the breast--metastasis or primary breast carcinoma? Case report].

A 74-year-old women with a history of neuroendocrine tumor in the terminal ileum presented on screening mammography with an irregular hypoechogenic mass in the upper outer quadrant of the left breast. A core biopsy showed a neuroendocrine tumor, interpreted as a probable metastasis from the intestinal primary. Other masses were found in the right lobe of the liver. Resection of the masses in the breast and liver was performed at the same time. Morphological and immunohistochemical findings (positive neuroendocrine markers, estrogene receptors and negative cytokeratine 7, mammaglobin, GCDFP-15, cytokeratine 20 and progesterone receptors) were consistent with a diagnosis of a metastatic well-differentiated neuroendocrine tumor, despite some estrogen receptor positivity. Issues of primary and metastatic breast neuroendocrine tumors are discussed in detail.