ESR1 and invasive breast carcinoma: In a case‐only analysis to investigate etiologic heterogeneity, mBCRS was more strongly associated with invasive breast cancer than DCIS (invasive, per covariate‐adjusted SD, HR: 1.90, 95% CI: 1.58, 2.29, P = 1.5 × 10−11; DCIS, HR: 1.50, 95% CI: 1.20, 1.89, P = 4.1 × 10−4; etiologic heterogeneity, P = 0.05); however, no differences were observed when comparing mBCRS and occurrence of estrogen receptor positive and negative invasive breast cancers (etiologic heterogeneity, P = 0.47; Table S7).