According to evidence resulting from the prospective randomized trial (TAILORx), OncotypeDx, based on the examination of the expression of 21 genes, is not only prognostic but also predictive of the efficacy of chemotherapy in ER+ HER2− pN0 breast cancers, and in general a recurrence score (RS) can be specified with which chemotherapy complementing endocrine therapy is not expected to have a significant effect, or above which chemotherapy has a survival benefit (85). Here, ESR1 is linked to breast cancer.