Metastatic Neuroendocrine Carcinoma Presenting with Bilateral Axillary Lymphadenopathy.

Metastatic, high-grade neuroendocrine carcinomas are frequently associated with small cell lung cancer (SCLC), classically spreading to the liver, bone, lung, and brain. Though SCLCs most commonly present as large masses interfering with the airway, this malignancy may appear initially as a benign mass at a distant site. This case profiles a 64-year-old woman who presented with bilateral breast masses that were identified as metastases of poorly differentiated, high-grade neuroendocrine SCLC through mammogram, ultrasound, CT, and core biopsy. Accurately identifying etiology of a breast malignancy is critical to therapeutic planning, as disparate treatment guidelines and disease courses exist for primary breast cancer and SCLC.