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Colonic carcinoid metastatic to the breast.

Metastatic tumors of the breast are uncommon. Breast metastases from nonmammary malignant neoplasms are rare, accounting for approximately 2% of all breast tumors. We report the case of an ileal carcinoid tumor metastatic to the breast 10 years after the initial diagnosis. A 53-year-old woman presented to our clinic with a palpable breast lump. The mammogram was nonspecific. A lumpectomy was performed that, on frozen section, showed a neoplastic lesion. Permanent sections showed that the tumor was composed of sheets of small uniform cells divided into lobules by delicate vascular septa. Immunohistochemical analysis showed that the lesional cells were strongly positive to the neuroendocrine marker panel of antibodies: chromogranin A, neuron-specific enolase, synaptophysin, serotonin, and low-molecular-weight keratin. The lesional cells were negative to cytokeratins 7 and 20, estrogen and progesterone receptors, carcinoembryonic antigen, and c-Erb-B2 antibodies. The presence of pleomorphic neurosecretory-type granules within the cytoplasm of the tumor cells by ultrastructural analysis strongly suggested a metastatic lesion from a midgut carcinoid. A detailed review of the patient's medical records confirmed a right hemicolectomy for an ileal carcinoid with lymph node and omental metastases that had been performed elsewhere 10 years earlier. A detailed pathologic analysis of this lesion by light microscopy, along with histochemical, immunohistochemical, and ultrastructural analyses, aided in confirming the metastatic nature of the current breast lesion.