ESR1 and breast cancer: Several smaller studies have shown a significant association between the Recurrence Score (RS) and pCR following NACT26–30 while a few have not31,32, and a significant association with pCR after NACT was shown for a high RS (OR 4.87, 95% CI 2.01, 1.82) in 898 ER-positive and HER2-negative breast cancer patients10.