Prospective Evaluation of a 12-gene assay on patient treatment decisions and physician confidence in mismatch repair proficient stage IIA colon cancer

Abstract Background The Onco type DX Colon Cancer Assay is a validated predictor of recurrence risk in patients with resected stage II colon cancer. We previously reported that Onco type DX led to a change in treatment recommendations for 45% of patients with T3 MMR-P stage II tumors in a prospective study. Here, we report the assay’s influence on patient treatment decisions, physician confidence, concordance between physicians and patients, and patient decisional conflict. Methods Consecutive patients with resected stage IIA colon cancer were enrolled. Tumor specimens were assessed by the 12-gene assay (RT-PCR) and MMR (IHC). Prior to and after receiving these results, patients completed surveys including their treatment preference, their current and preferred roles in treatment decision-making, and indicators of decisional conflict. Physicians completed similar pre- and post-assay survey items. Results Out of 221 enrolled, 139 T3 MMR-P patients were evaluable for patient reported analyses and 150 patients were evaluable for physician-reported analyses. Pre-assay: 46% of patients chose Observation, 3% 5FU, 7% Oxaliplatin, 4% Other and 41% were undecided. Post-assay: 75% chose Observation, 12% 5FU, 11% Oxaliplatin, and 2% Other. Post-assay, 94% of defined treatment decisions were concordant between patients and physicians compared to 60% pre-assay. Physicians reported the assay influenced their treatment decisions and increased confidence in treatment recommendations for 69% and 84% of patients, respectively. The majority of patients (86%) reported that the assay influenced their treatment decisions. Patient decisional conflict was significantly lower after learning the assay results (p < 0.001). Conclusions In this prospective study, knowledge of the 12-gene assay results influenced treatment decisions for most patients and physicians, increased physician confidence, improved concordance between patients and physicians, and decreased patient decisional conflict.