ESR1 and breast cancer: The associations between HR status of first tumor and CBC risk were not modified by either first-degree breast cancer family history (any family history ER-/PR- vs. ER+/PR+ RR = 1.5, 95% CI 1.1–2.3; no family history RR = 1.3, 95% CI 1.0–1.7, Pheterogeneity = 0.43) or diagnosis age (<45 years ER-/PR- vs. ER+/PR+ RR = 1.4, 95% CI 1.0–1.8; ≥45 years RR = 1.3, 95% CI 1.0–1.7, Pheterogeneity = 0.79).