Background: Tumor microenvironment plays a critical role for CRC development and progression. CAFs are the most dominant cellular components which orchestrate tumor cell proliferation, survival and invasion and have been shown to be associated with prognosis in pts with CRC. We aimed to evaluate whether single-nucleotide polymorphisms (SNPs) in CAFs related genes predict outcome in mCRC pts treated with first-line FOLFIRI/bevacizumab (bev) in TRIBE and FIRE-3 trials. Methods: The OncoArray, a custom array by Illumina including 530K SNP markers, was used to genotype genomic DNA from blood samples and served as our database, from which 15 functional SNPs within 9 genes (OPN, CD44, TCN, CD63, TIMP1, SLIT2, ROBO1, LOXL2, INHBA) related to CAF pathway were analyzed. Results: A total of 451 pts were included. Those treated with FOLFIRI/bev in TRIBE (N = 215, median PFS/OS: 9.7/26.3 months (mts)) and FIRE-3 (N = 107, median PFS/OS: 11.6/31.5 mts) served as discovery and validation cohorts respectively, while FIRE-3 FOLFIRI/cetuximab arm (N = 129, median PFS/OS: 12.8/49.8 mts) was used as the control. In overall pts in discovery set, OPN (osteopontin) rs11728697 any C variants showed longer PFS (median 10.8 vs 9.0 mts; HR = 0.68, 95%CI = 0.49-0.95; p = 0.025) and OS (median 30.6 vs 23.8 mts; HR = 0.69, 95%CI = 0.50-0.95; p = 0.025) than the homozygous wild type genotype (T/T) in multivariable analysis. These data were validated in the FIRE-3 cohort in OS both in univariate (median 49.3 vs 23.7 mts; HR = 0.40, 95%CI = 0.21-0.77; p < 0.001) and in multivariable analyses (HR = 0.31, 95%CI = 0.16-0.60; p < 0.001). However, the favorable impact on outcome was not shown among C allele carriers treated with FOLFIRI/cetuximab in the control arm. Conclusions: Our findings confirm that CAFs play a crucial role in mCRC and suggest that OPN polymorphisms could serve as predictive biomarkers for mCRC pts treated with first-line FOLFIRI/bev.