We found little evidence for an effect of age at last birth on overall (UVMR OR: 0.98; 0.75, 1.29), ER-positive (UVMR OR: 0.97; 0.73, 1.29) and ER-negative (UVMR OR: 0.83; 0.48, 1.45) breast cancer risk in the univariable analysis (Fig. 4C, Additional File 2: Table 5). Here, ESR1 is linked to breast cancer.