A rare type of breast cancer that makes hormones can shrink dramatically when treated with a mix of hormone blockers (letrozole and triptorelin) plus a cell‑cycle drug (palbociclib). This case shows that targeting estrogen signals together with stopping cells from dividing may work well as a first treatment, but it’s based on one patient and needs doctor oversight.

There is no consensus regarding the therapeutic approach of breast neuroendocrine carcinomas (NECs). As most NECs are hormone receptor positive and HER-2 negative, we suggest that endocrine-based strategies may play a leading role. Here, we report a new treatment strategy by incorporating CDK4/6 inhibitors in the therapeutic armamentarium. Primary neuroendocrine neoplasms of the breast constitute a rare entity. They are characterized by predominant neuroendocrine differentiation and are further divided into well-differentiated neuroendocrine tumors and poorly differentiated (high-grade) neuroendocrine carcinomas (NECs). Regarding their therapeutic approach, there are no standardized guidelines. Herein, we present the first case ever reported, concerning a female patient with de novo metastatic breast NEC who received hormonal therapy, a combination of a CDK4/6 inhibitor palbociclib with letrozole and triptorelin, as first-line treatment with significant clinical and radiological response. As most NECs are estrogen receptor and/or progesterone receptor positive and HER-2 negative, we suggest that hormonal therapy may play a leading role even in the first-line setting. The present report provides a new treatment strategy by incorporating CDK4/6 inhibitors in the therapeutic armamentarium of breast NECs.