Oncotype DX testing does not affect clinical practice in stage IIa colon cancer

Although studies have demonstrated the 12-gene Oncotype DX Colon Recurrence Score's (RS) validity in predicting recurrence and influence on physician-patient decision-making, its discriminatory power and inability to predict response to treatment make its clinical impact uncertain. We sought to evaluate the influence of RS in the decision to offer adjuvant chemotherapy after resection of stage IIa colon cancer. A review of patients with stage IIa colon cancer who obtained the RS at a tertiary academic medical center was conducted. The main study outcome was decision to start adjuvant chemotherapy. The association between RS and the decision to obtain adjuvant chemotherapy was evaluated utilizing the Wilcoxon rank-sum test and area under the receiver operating characteristic curve. 52 of 105 patients with stage IIa colon cancer underwent RS testing. Overall, seven of 52 patients (13%) received adjuvant chemotherapy. 34 (65%) patients obtained the RS test despite having multiple other recurrence risk factors. There were no significant associations between any patient/tumor characteristic and RS score (all p > 0.08) or starting adjuvant chemotherapy (all p > 0.15). On multivariable analysis, there was no significant effect of RS on the odds of undergoing chemotherapy (OR 1.07, 95% CI 0.98-1.19; p = 0.14). There was no clear association between RS and starting adjuvant chemotherapy (AUC 0.64, 95% CI 0.36-0.91; p = 0.25). RS was not associated with the decision to start adjuvant chemotherapy. Given its lack of association with clinical decision-making and inability to predict clinical outcome, our data suggest the RS should not be obtained in patients with stage IIa colon cancer.