CDK4/6 and aromatase inhibitors as first-line treatment in metastatic high-grade neuroendocrine carcinoma of the breast: A case report.

Key Clinical Message: 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. Abstract: 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.