Validation of a quantitative 12-multigene expression assay (Oncotype DX(®) Colon Cancer Assay) in Korean patients with stage II colon cancer: implication of ethnic differences contributing to differences in gene expression

PURPOSE: To evaluate the Recurrence Score(®) of the quantitative 12-multigene expression assay and to determine risk groups based on the continuous Recurrence Score(®) in Korean patients. METHOD: A total of 95 patients with pathological T3N0 tumors and mismatch repair-proficient tumors were enrolled. The Recurrence Score(®) was used to classify risk groups (low risk, <30; intermediate risk, 30–40; high risk, ≥41). RESULTS: Fifty-four patients (56.8%) were aged over 70 years. There were 49 men (51.6%) and 56 cases of right-sided colon cancer (58.9%). Eight cases (8.4%) had well-differentiated tumors, and 86 cases (90.5%) showed moderate differentiation. Only one case (1.1%) had a poorly differentiated tumor. Three patients (3.2%) had lymphovascular invasion. Sixty-one patients were identified as low risk (64.2%) and 34 patients as intermediate risk (35.8%). There were no high-risk patients. Although not significant, the 3-year recurrence risk increased with the Recurrence Score(®). CONCLUSION: Distribution patterns of risk groups based on the Recurrence Score(®), particularly the absence of a high-risk group, were different from the prior validation studies. These findings suggest that ethnic differences between Koreans and Western patients are potential contributing factors for different gene expressions in the quantitative 12-multigene expression assay.