Background: Standard 1L mCRC treatment (tx) includes a CT backbone (e.g. modified leucovorin [LV]/5-fluorouracil [5-FU]/oxaliplatin [mFOLFOX6] or LV/ 5-FU/ irinotecan [FOLFIRI]) and a biologic (e.g. BV). The preferred CT backbone for anti-VEGF tx is unknown. MAVERICC (NCT01374425), a global, randomized, open-label, phase 2 trial, assessed efficacy and safety of mFOLFOX6-BV vs FOLFIRI-BV in pts with mCRC. PFS and OS were comparable between FOLFIRI-BV and mFOLFOX-BV (Lenz et al, ASCO GI 2016). Exploratory analyses compared clinical outcomes of the BV-containing tx groups by primary tumor location and baseline (BL) KRAS status. Methods: Pts with mCRC (≥1 measurable metastatic lesion, ECOG performance status ≤1) were randomized 1:1 to BV (5 mg/kg) + mFOLFOX6 or FOLFIRI every 2 wks. Time to PFS and OS for each tx group were estimated by Kaplan–Meier methods, hazard ratios (HR) were estimated by Cox regression, p-values were based on log-rank tests stratified by BL ERCC-1 status and region. Results: 376 pts were randomized: median age, 61 yr; white race, 83%; US region, 85%. BL: KRAS mutant (MUT), 34%; KRAS wild type (WT), 55%; KRAS unknown, 11%; left-sided primary tumor, 59%. Efficacy results are shown. Conclusions: There was a trend toward improved PFS and OS in the FOLFIRI-BV group, regardless of primary tumor location or BL KRAS status. PFS benefit from FOLFIRI-BV was statistically significant in left-sided tumors only. PFS and OS were numerically greater in pts with WT vs MUT KRAS status. Clinical trial information: NCT01374425

^a FOLFIRI vs mFOLFOX6 ^bp=0.040, others p>0.05 ^cKRAS status of 40 pts unknown