The BRCA1 carriers tend to develop estrogen receptor-negative breast cancers which do not depend on estrogen to grow, and the BRCA2 carriers tend to develop breast cancers that are estrogen receptor-positive and depend on estrogen to grow.19–21 Chemoprevention with tamoxifen has not been shown to prolong survival in BRCA2 carriers.17,18 Oral contraceptive pills have been shown to reduce the chances of developing ovarian cancer in BRCA carriers by 50% without increasing the risk of breast cancer, but this intervention has not been shown to reduce the chances of dying of ovarian cancer.22 Here, ESR1 is linked to breast cancer.