Adrenocorticotropic Hormone-producing Extrapulmonary Small Cell Carcinoma of the Breast.

Extrapulmonary small cell carcinoma (EPSCC) of the breast is a very rare tumor. Adrenocorticotropic hormone (ACTH) production from these tumors is extremely rare and seldom reported resulting in significant diagnostic and therapeutic challenges and delays. We present a case of a 38-year-old female who presented with a breast lump and was diagnosed with primary EPSCC of the breast. Eighteen months later, she presented with refractory hypokalemia and metabolic alkalosis. Ectopic ACTH production was found to be the reason for her metabolic derangement. Extensive diagnostic evaluation, including a comprehensive metastatic workup, is necessary to differentiate this tumor from other primary malignancies such as lung and other breast cancers. We review the literature and discuss the diagnostic approach and suggested therapies.