Background: MOSAIC and C-07 showed that oxaliplatin (OX) added to 5-fluorouracil plus leucovorin significantly improved disease free survival (DFS). However, OX is associated with neurotoxicity and the vast majority of patients do not receive OX-benefit; highlighting the importance of an OX-benefit predictor. In C-07, colon tumors with a CRCA (Colorectal Cancer Assigner) stem-like subtype were associated with a poor prognosis and no OX-benefit, but stage III patients with an enterocyte subtype did. We tested the association of CRCA and CMS molecular subtypes with prognosis and OX-benefit in stage III MOSAIC patients. Also, recombination proficiency scores (RPS) were tested for the same associations. RPS scores quantify the efficiency of DNA-damage repair. Low RPS have been associated with inferior overall survival (OS) in non-small cell lung carcinoma patients treated with surgery alone but better OS for patients who received surgery plus chemotherapy. Methods: Gene expression profiles from 590 stage III pts with follow up were successfully profiled by a custom designed nCounter code set. CRCA subtypes were determined by a locked down algorithm based on a re-estimated centroid using 72 genes (Song et al 2016). CMS subtypes were determined by modified single sample predictor (SSP) using 84 genes. RPS scores were determined as previously described by Pitroda et al (2014). Signature predictions were made while blinded to clinical outcome and signature performance was evaluated while blinded to gene expression. Results: The stem-like subtype was associated with a very poor prognosis (Stem-like vs others HR=1.56, p<0.01) and no OX-benefit. CRCA and CMS subtypes did not associate with OX-benefit. Using a median cut point, stage III patients with low RPS scores received significant OX-benefit (HR=0.67, p=0.033, N=290) and patients with high RPS scores did not (HR=1.2, p=0.32, N=300) with significant interaction p=0.025. Conclusions: The observation in C-07, that the stem-like subtype has the poorest prognosis and did not receive OX-benefit, was validated in MOSAIC, identifying patients who need new therapies. RPS scores may help to identify the subset of patients with OX-benefit in stage III CC, confirmation of this observation is currently being investigated in C-07. Support: PA DoH; NSABP; Sanofi.