ESR1 and neoplasm: Variables adjusted for were all available, non-redundant factors for each dataset as follows: METABRIC, patient age at diagnosis, disease stage, tumor grade, ER status (positive or negative), PR status (positive or negative), HER2 status (positive or negative), and non-surgical treatment status (whether the patient received treatment beyond surgery); Ur-Rehman and Vijver: patient age at diagnosis, tumor size, tumor grade, lymph node status (positive or negative), ER status (positive or negative), and non-surgical treatment status (whether the patient received treatment beyond surgery).