Neoadjuvant endocrine therapy for estrogen receptor-positive primary breast cancer

Neoadjuvant endocrine treatment (NAE) for estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative primary breast cancer improves the surgical outcome, and its therapeutic response is useful for predicting prognosis. The indication for NAE is patients who have highly hormone-sensitive breast cancer. The optimal treatment duration depends on the required endpoint. In the case of tumor reduction or introduction to breast-conserving surgery (BCS), a treatment period of at least 6 months is required. Several clinical trials are underway to develop treatment strategies based on shortterm responsiveness to NAE to improve the prognosis of hormone receptor (HR)-positive/HER2-negative breast cancer. This article outlines the current status of NAE and new treatment strategies based on the responsiveness during NAE or clinical and biological feature on residual tumor after NAE.