Racial variation in adjuvant chemotherapy initiation among breast cancer patients receiving oncotype DX testing

It is unknown whether racial differences exist in adjuvant chemotherapy initiation among women with similar oncotype DX (ODX) risk scores. We examined whether adjuvant chemotherapy initiation varied by race. Data come from the Phase III, Carolina Breast Cancer Study, a longitudinal, population-based study of North Carolina women diagnosed with breast cancer between 2008 and 2014. We used modified Poisson regression and report adjusted relative risk (aRR) and 95 % confidence intervals (95 %CI) to estimate the association between race and adjuvant chemotherapy initiation across ODX risk groups among women who received the test (n = 541). Among women who underwent ODX testing, 54.2, 37.5, and 8.3 % of women had tumors classified as low-, intermediate-, and high-risk groups, respectively. We observed no racial variation in adjuvant chemotherapy initiation. Increasing ODX risk score (aRR = 1.39, 95 %CI = 1.22, 1.58) and being married (aRR = 2.92, 95 %CI = 1.12, 7.60) were independently associated with an increased likelihood of adjuvant chemotherapy in the low-risk group. Among women in the intermediate-risk group, ODX risk score (aRR = 1.15, 95 %CI = 1.11, 1.20), younger age (aRR = 1.95, 95 %CI = 1.35, 2.81), larger tumor size (aRR = 1.70, 95 %CI = 1.22, 2.35), and higher income were independently associated with increased likelihood of adjuvant chemotherapy initiation. No racial differences were found in adjuvant chemotherapy initiation among women receiving ODX testing. As treatment decision-making becomes increasingly targeted with the use of genetic technologies, these results provide evidence that test results may drive treatment in a similar way across racial subgroups.