The use of ‘selective ER modulators’ (SERMs) or ’degraders’ (SERDs), such as tamoxifen (Tam) and fulvestrant, respectively, as well as of aromatase inhibitors (AIs), e.g., anastrozole, significantly improved both the relapse-free survival (RFS) and the overall survival (OS) of ER + BC patients. The gene discussed is ESR1; the disease is breast cancer.