ESR1 and breast carcinoma: Breast cancer is still the most common cancer in women worldwide,affecting one in eight women in high-income countries, and the incidenceis further increasing.1 The majority ofall types of mammary carcinomas (MCs) are, at least initially, hormone-dependent.2,3 Endocrine therapy, including aromatase inhibitors or selective estrogenreceptor modulators (SERMs)/selective estrogen receptor downregulators(SERDs), consequently represents an indispensable treatment opportunity.Unfortunately, acquired endocrine resistance is an inevitable issue,which manifests after prolonged therapy.4,5