Data from the NSABP (the National Surgical Adjuvant Breast and Bowel Project) B14 and B20 patients with node negative, ER+/HER2- breast cancer suggest that besides quantifying the likelihood of distant recurrence (prognostic value) within ten years of the initial diagnosis [3], the RS assay estimates the magnitude of chemotherapy benefit (predictive value) [4]. The gene discussed is ESR1; the disease is breast carcinoma.