Therefore, two major therapeutic approaches are involved in breast cancer treatment and prevention: the first involves the development of drugs that target the estrogen receptor, which are also known as selective estrogen receptor modulators (SERMs), whereas the second approach involves the development of drugs that target aromatase (i.e., the enzyme that converts androgens to estrogens) and are thus known as aromatase inhibitors (AIs). Here, ESR1 is linked to breast cancer.