ESR1 and ductal breast carcinoma in situ: It is used (1) to treat estrogen receptor-positive (ER+ve) metastatic breast cancer; (2) as an adjuvant to treat patients with early stage ER+ve breast cancer; (3) to decrease the risk of invasive breast cancer after tumor excision and radiation in women with ductal carcinoma in situ (DCIS); and (4) to decrease the incidence of breast cancer in women at high risk [37,38].