ESR1 and breast cancer: Excluding these women attenuated the increased RRs for CBC observed among all women when comparing HR+ to HR- first breast cancers, but the increased risk of ER-/PR- CBC following a diagnosis of an ER-/PR- first tumor, compared to an ER+/PR+ first tumor, persisted (all tested women RR = 7.6, 95% CI 3.0–19.5; non-carriers RR = 7.7, 95% CI 2.6–23.3) (Table 5).