ESR1 and breast cancer: Interestingly, there was a suggestion of an rs299290 association with ERα-negative breast cancer for BRCA2 mutation carriers, but in the opposite direction to that observed for BRCA1 mutation carriers: ERα-negative BRCA2 mutation carriers n = 434, per-allele HR = 0.83, 95% CI 0.70–0.97, p = 0.022.