Currently, chemoprevention for high-risk women, including those with a five-year breast cancer risk of ≥1.7% or personal history of atypical hyperplasia or lobular carcinoma in situ, may include a selective estrogen receptor modulator (SERM) such as tamoxifen or an aromatase inhibitor such as exemestane (postmenopausal women only). Here, ESR1 is linked to breast cancer.