Previously reported studies included cohorts which: were ERα negative with the majority being triple negative breast cancers [21], contained both ERα + and ERα- cases with the majority being defined as low risk (small tumor size and node negative) [32], had no information available concerning therapies [30], consisted of mainly familial breast cancer cases where few are ERα + [29] or consisted of a cohort in which only 50% of tumors were ERα+, or more than 60% of the women were under 50 years of age [31]. Here, ESR1 is linked to breast cancer.