ESR1 and breast cancer: ERα-positive BC is treated with adjuvant endocrine therapy (AET), which comprises selective ERα modulators (SERMs, e.g., tamoxifen), selective ERα degraders (SERDs, e.g., ICI182,780) and aromatase inhibitors (AIs, e.g., anastrazole), with tamoxifen for five years considered a treatment of choice for a large fraction of early-stage ERα-positive BC cases [2].