Introduction/Background Pancreatic neuroendocrine tumors (PNETs) are an uncommon malignancy, accounting for a small percentage of all pancreatic malignancies. Although, reports in the literature describe PNET metastasis to the liver, lung and brain, there are very few reports of stage IV disease involving the breast. We report a case of a woman with a history of pancreatic PNET, misdiagnosed as primary breast cancer.

Methodology A 38-year old woman underwent a wide lumpectomy of her right breast, which was misdiagnosed as a triple negative, apocrine carcinoma of the breast. Clinical history was not known, at the time.

Results Following the information of the clinical history of the patient, with metastatic pancreatic PNET in the liver, lung, adrenal gland, lymph nodes and bones, review of the architectural/cytological features of the tumor along with immunohistochemical staining with breast and neuroendocrine markers took place, which showed negative staining for breast markers and positive staining for neuroendocrine markers. Morphology and immunophenotype were compatible with secondary neuroendocrine carcinoma, of pancreatic origin.

Conclusion Suspicion for metastasis must be high in breast tumors with morphologic unusual features/patterns and in low-grade, non-gland forming tumors that are estrogen receptor, progesterone receptor and HER-2/neu (triple) negative, as a metastasis to the breast can be the presenting sign of a neuroendocrine tumor elsewhere in the body in nearly one-third of the reported cases, or show similar morphologic features with the primary tumors. Increased awareness, the clinical history and review of prior slides are vital for the correct diagnosis, as treatment for metastatic lesion is significantly different from treatment of a primary breast tumor, as radiation to the breast and lymph node sampling may not indicated and systemic therapies will likely be considered if the correct diagnosis can be made.

Disclosure Nothing to disclose.