The 21-gene recurrence score (RS) assay provides both prognostic information for distant recurrence (DR) and predictive information for chemotherapy benefit in hormone receptor–positive, human epidermal growth factor receptor 2 (HER2)–negative early breast cancer.1-5 The relative risk reduction with chemotherapy increases with increasing RS result, and the absolute magnitude of chemotherapy benefit also varies with the underlying recurrence risk,6 which is associated with both clinical-pathological features and RS result.7 Here, ERBB2 is linked to breast cancer.