ESR1 and breast cancer: Building on these results, KEYNOTE-756 (NCT03725059) was designed as a randomized, double-blind, phase 3 study to evaluate the efficacy and safety of neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab plus endocrine therapy versus neoadjuvant placebo plus chemotherapy followed by adjuvant placebo plus endocrine therapy in patients with high-risk, early-stage, ER+/HER2− breast cancer.