ESR1 and breast carcinoma: For instance, although the Oncotype DX test (Oncotype IQ) is informative, the decision regarding systemic therapy remains challenging for clinicians for more than 50% of patients with estrogen receptor–positive early breast cancer.26,27 Moreover, the routine use of Ki67 in clinical practice has been limited by the lack of its standardization assessment28 and by its lack of success in treatment decision-making in several clinical trials.29,30