Supplementary Material for: A Validation Study for Recurrence Risk Stratification of Stage II Colon Cancer Using the 55-Gene Classifier

Introduction: DNA microarrays, such as the consensus molecular subtype (CMS) classification using >600 genes, are used to predict cancer patient prognosis. We recently constructed a simple 55-gene classifier (55GC) system to risk stratify colon cancer (CC). Objective: Here, we validate the 55GC specifically for stage II CC and compare it with CMS categories. Methods: Tissue sections from 232 stage II CC patients who underwent curative surgery without adjuvant chemotherapy between 2009 and 2012 were subjected to DNA microarray analysis. Results: Based on the 55GC, patients were classified into microsatellite instability-like (27%), chromosomal instability-like (41%), and stromal (32%) subtypes with 5-year relapse-free survival (RFS) rates of 88.5, 83.3, and 71.2%, respectively (stromal vs. others: p = 0.0049). Multivariate analysis by Cox’s proportional hazard model revealed that the stromal subtype, pT4, and the number of lymph nodes examined (<12) were independent poor prognostic factors. The overall concordance rate between 55GC and CMS was 72%, and 5-year RFS rates of patients with CMS1, CMS2, CMS3, and CMS4 cancers were 100, 85.5, 92.3, and 73.0%, respectively (p = 0.0113). Conclusions: We conclude that the 55GC is a useful and reproducible grading system for stage II CC recurrence risk stratification.