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.