Routine Screening Mammogram Leading to the Incidental Diagnosis of a Metastatic Neuroendocrine Breast Cancer (NEBC) from an Unrecognized Asymptomatic Small Bowel Neuroendocrine Tumor

Neuroendocrine neoplasms (NENs) are epithelial neoplasms with predominant neuroendocrine differentiation that arise in the gastrointestinal tract, unique to the site of origin, such as the pancreas and small intestine. Neuroendocrine breast carcinoma (NEBC) is a rare tumor. Diagnosing NEBC is challenging because there is no specific clinical presentation, as it is usually presented as a breast lump. Therefore, diagnosing NEBC before biopsy is difficult. Another challenge in diagnosing NEBC is to know whether it is primary or metastatic. We present a case of a 60-year-old woman found to have a solid left breast nodule during routine screening mammography. Tissue biopsy was found to be consistent with metastatic NEBC. The patient was found to have primary small intestine asymptomatic NENs on further diagnostic tests. Eventually, she had a lumpectomy and started on lanreotide (Somatuline) intramuscular monthly injections. As per literature, metastatic NEBC is infrequent. It was considered a poor prognostic breast tumor, as it is usually presented as hormonally negative breast cancer. Management of metastatic versus primary NEBC is still more controversial. Gastroenteropancreatic NENs are treated with long-acting somatostatin analogs with good prognostic results.