Outcomes after chemotherapy in early-stage breast cancer (EBC) patients who underwent a 21-gene expression assay.

559Background: A recent report from the Trial Assigning Individualized Options for Treatment (TAILORx) study showed that EBC patients who had hormone receptor-positive (HR+), human epidermal growth factor receptor type 2-negative (HER2-), axillary lymph node-negative (LN-) tumors with a recurrence score (RS) of 0-10 in a 21-gene expression assay, had a high rate (93.8%) of invasive disease-free survival (IDFS) at 5 years when treated with endocrine therapy alone. However, outcomes after chemotherapy among patients with a RS of 11-25 were not reported. Methods: We performed a retrospective study of women with HR+ HER2- LN- EBC who received treatment at MD Anderson from 2005-2014 and had a 21-gene expression assay performed at diagnosis. We used a Kaplan-Meier method to estimate the IDFS rate at 5 years, and a multivariable Cox proportional hazards model to calculate a hazard ratio (HR) and 95% confidence interval (CI), assessing the effect of chemotherapy for IDFS, recurrence-free survival (RFS), distant-r...