ESR1 and breast cancer: The Optimal Personalised Treatment of early breast cancer using Multiparameter Analysis preliminary study (OPTIMA prelim) compared risk stratification and subtype classification of five multigene predictor tests (Oncotype DX, Prosigna [PAM50], MammaPrint, MammaTyper, and NexCourse Breast [IHC4-AQUA]) performed in a series of 313 women with ER+/HER- early breast cancer that were randomized to chemotherapy and endocrine therapy or test-directed (chemotherapy if Oncotype DX RS >25) treatment [15].