693 Background: The benefits of anti-cancer treatment must be balanced with the impact of adverse events on QoL. In the PRIME study, first-line pmab + FOLFOX4 significantly improved overall survival vs. FOLFOX4 in patients (pts) with RAS WT (KRAS/NRAS WT exons 2, 3 and 4) mCRC, but was associated with typical EGFR inhibitor adverse events. Here we report pre-specified tertiary QoL endpoints for pts with RAS WT mCRC. Methods: PRIME was a randomised open-label phase III study of first-line pmab 6.0 mg/kg Q2W + FOLFOX4 vs. FOLFOX4 in mCRC pts. QoL was assessed every 4 weeks until disease progression, and once at safety follow-up, using the EuroQoL 5-domain (EQ-5D) health state index (HSI) and overall health rating (OHR; 0–100 visual analogue scale). Differences were assessed from baseline to disease progression, and to discontinuation of first-line treatment, using analysis of covariance (ANCOVA) and a mixed-effect piecewise linear model. Analysis of QoL by skin toxicity severity is also planned. Results: 50...