21-Gene Recurrence Score Assay As a Predictor of Adjuvant Chemotherapy Administration for Early-Stage Breast Cancer: An Analysis of Use, Therapeutic Implications, and Disparity Profile

PurposeThe 21-gene Recurrence Score (RS) assay is used to predict disease recurrence and benefit of chemotherapy in estrogen receptor–positive, lymph node–negative early-stage breast cancer (EBC). Our study is the first analysis of trends and differences in the use of the RS assay and its impact on recommending chemotherapy in a population-based data set.MethodsPatients with EBC diagnosed from 2004 to 2012 and included in the National Cancer Data Base were analyzed. Multivariate logistic regression analysis was used to estimate the covariates associated with use of the test and its impact on chemotherapy decisions.ResultsThe RS assay was ordered for 54.0% of the 143,032 identified patients. Of all the variables, RS assay had the strongest association with recommendation for chemotherapy, with an adjusted odds ratio (AOR) of 83 for high assay scores. When indicated, test use was significantly associated with younger age, white race, academic centers, private insurance, and pT2/pN0(i+) grade 2 to 3 disease....