High grade neuroendocrine carcinoma of the breast, first line and maintenance immunotherapy.

Small cell carcinomas (SCCs) are poorly differentiated neuroendocrine tumors that arise predominantly in the lung and gastrointestinal tract (GIT). Neuroendocrine carcinomas can occur in a variety of extrapulmonary sites throughout the body, including breast, larynx, GIT, prostate, urinary bladder, ovary and cervix. This is a case report of a 55-year-old Asian female patient with metastatic high-grade neuroendocrine carcinoma of unknown origin that responded notably to off-label nivolumab maintenance treatment after first-line carboplatin - etoposide chemotherapy and radiation. After 2 years of nivolumab after platinum-based chemotherapy results from PET-CT showed no residual disease and we proceeded to mastectomy.