ESR1 and breast cancer: Our MR suggested that any migraine (AM) was a risk factor for overall breast cancer (IVW: odds ratio (OR) = 1.072, 95% confidence intervals (CI) = 1.035–1.110, P = 8.78 × 10− 5, false discovery rate (FDR) = 7.36 × 10− 4) and estrogen receptor-positive (ER+) breast cancer (IVW: OR = 1.066, 95% CI = 1.023–1.111, P = 0.0024; FDR = 0.0108) but not estrogen receptor-negative (ER-) breast cancer.