S2960 Incidental Diagnosis of a Rare Metastatic Neuroendocrine Breast Cancer During Routine Screening Mammogram Which Eventually Revealed Primary Small Intestine Carcinoid Tumor

Abstract

Introduction: Neuroendocrine neoplasms (NENs), defined as epithelial neoplasms with predominant neuroendocrine differentiation, typically occur in the pancreas, tubular gastrointestinal tract, or lung with or without secretory syndromes. Neuroendocrine breast carcinoma (NEBC) is a rare tumor which accounts for 1-2% of all invasive breast carcinoma. When NENs are found on a biopsy of a breast nodule it is considered either primary NEBC or metastatic if another primary organ is discovered. NEBC usually presents as a breast lump on exam without neuroendocrine symptoms. Therefore, making a diagnosis of NEBC prior to biopsy is difficult. We present a case of an incidentaloma discovered on routine mammography that turned out to be NEBC on biopsy and further evaluation discovered an asymptomatic primary small bowel NEN, thus confirming the breast as metastatic NEBC. Case Description/Methods: A routine mammogram in 60 yo. female revealed an abnormal 4 mm solid nodule in the right breast. A core needle biopsy found a low grade, well differentiated NEN, with positive staining for synaptophysin and chromogranin. She felt well and denied any symptoms. Medical history was notable for immune hepatitis with liver cirrhosis managed by her hepatologist. An abdominal MRI/MRCP revealed thickening in the small bowel wall consistent with a primary carcinoid tumor and demonstrated hepatic surface metastases. Plasma and 24 hr. urine 5 HIAA and chromogranin A plasma levels were normal. A lumpectomy was performed and therapy with lanreotide i.m. monthly injections begun. At 6 months follow-up, she remains asymptomatic, with stable disease. Discussion: Metastasis to the breast from a primary NEN is infrequently reported in the literature. If discovered in a patient without a history of known primary NEN in another organ, imaging is warranted to seek asymptomatic and non-secreting tumors elsewhere, as in the GI tract of our patient. No proven effective chemotherapy or RT for either primary or metastatic NEBC exists. No proven effective chemotherapy regimen exists for NENs, but therapy with long-acting somatostatin analogs are the preferred first-line option for NENs associated with several hormonal syndromes as well as for growth control in well-differentiated unresectable or metastatic gastroenteropancreatic NENs as in our case.