BRCA1 and breast cancer: A majority of breast cancers among BRCA1-mutation carriers are oestrogen-receptor negative (Foulkes et al., 2004), and removal of ovaries in BRCA1-mutation carriers with an oestrogen-receptor negative breast cancer dramatically reduces breast cancer-specific mortality (hazard ratio 0.07, p = 0.009) (Metcalfe et al., 2015), suggesting that breast cancer biology in BRCA1-mutation carriers is determined by ovarian hormones other than oestrogens.