Background: An 18-gene expression profile, ColoPrint, has been developed for identifying colon cancer patients more likely to develop recurrent disease and who would be candidates for adjuvant chemotherapy. The gene signature was validated in public datasets and independent patient cohorts (stage II and III patients). Uni-and multivariate analysis was performed on the pooled stage II patient set (n=320) (median follow-up 70 months). ColoPrint classifies 65% of stage II patients as Low Risk. The 3-year RFS was 91% for Low Risk and 74% for High Risk patients with a HR of 2.9 (p=0.001). ColoPrint was the only significant prognostic marker in the subgroup of patients with T3-MSS phenotype (Tabernero, ASCO GI 2012). Methods: A blinded prospective trial, PARSC (Prospective study for the Assessment of Recurrence risk in Stage II colon cancer patients) using ColoPrint has been initiated. Objectives are: (1)To validate the performance of ColoPrint in estimating the 3-year relapse rate in patients with stage II colon cancer. (2) To compare the risk assessment in stage II patients using the ColoPrint profile vs a clinical risk assessment based on Investigator’s assessment of risk and ASCO high-risk recommendations. (3) To investigate therapy as a potential confounding factor for ColoPrint results. (4) To assess the performance of ColoPrint in estimating the 3-year relapse rate in patients with stage III colon cancer. Inclusion criteria: age ≥ 18 years, adenocarcinoma of the colon, stage II and III, no prior neo-adjuvant therapy, no synchronous tumors, fresh tumor sample, and written informed consent. The treatment of the patient is at the discretion of the physician adhering to National Comprehensive Cancer Network (NCCN)-approved regimens or a recognized alternative (blinded for ColoPrint result). The trial started in Sept. 2008 with currently 32 participating sites in 11 countries. Thus far, 340 eligible stage II and 280 stage III patients have been enrolled. The aim is to enroll 575 stage II patients. Clinical trial registry number: NCT00903565.