ESR1 and breast cancer: Furthermore, as demonstrated in two independent cohorts, ER+ BC patients in the high-risk group had a much lower pathological complete response (pCR) rate than those in the low-risk group after receiving neoadjuvant chemotherapy (6.7% versus 13.4% in GSE25066; 15.0% versus 40.0% in GSE4779) (Figure 6D).