ESR1 and breast cancer: In ER + HER2− breast cancer, IRSN-23 Gp-R (OR = 28.54, P = 0.009), HRD ≥ 42 (OR = 20.14, P = 0.006), and Oncotype Dx RS > 25 (OR = 18.74, P = 0.014) were all significantly associated with pCR (Fig. 2B).