Background: Wnt signaling pathway genes TCF7L2 and AXIN2 complex control the proliferation and differentiation of intestinal epithelial cells. Our previous study showed that TCF7L2 and AXIN2 polymorphisms(SNPs) were associated with clinical outcome of mCRC patients(pts) treated with first line FOLFIRI/BEV from TRIBE (arm A) and PROVETTA trials (n=455) (ASCO 2013#3566). Our data demonstrated that the association of TCF7L2rs7903146 and AXIN2 rs2240308 snps with PFS and OS is depended on gender and location. The goal of the current study was to prospectively validate our previous findings in mCRC pts enrolled in FIRE-3 clinical trial, which treated with either first line FOLFIRI/BEV or FOLFIRI/cetuximab. Methods: Genomic DNA was isolated from tissue samples of 592 pts (patient characteristics gender, median age median follow up) treated with first-line FOLFIRI/ bevacizumab (n=295) or FOLFIRI cetuximab (n=297) from the FIRE-3 trial (NCT00433927). All pts were KRAS exon 2 wild-type. The bevacizumab arm served as validation arm whereas the cetuximab arm served as control arm. Results: Our data validated that TCF7L2rs7903146 and AXIN2 rs2240308 snps could predict clinical outcome when adjusted by pts gender and tumor location. 1) In right-sided tumors, Female pts with any T allele of TCF7L2rs7903146 were associated with significantly longer PFS(median=13 mos) (HR: 0.38; 95% CI: 0.15, 0.97) in comparison to those carrying C/C genetype(median=5.7 mos, P = 0.04), which is consistent with our previous data. 2) In left-sided tumors, Female pts with AXIN2 rs2240308 any A allele had shorter OS(median=24.8 mos)(HR: 2.87; 95% CI: 1.07,7.76; P = 0.026) compared to those with G/G variants(median=44.3 mos), which validated our previous data. No significant difference in control arm. Conclusions: In this study, we prospectively validated the predictive value of TCF7L2 rs7903146 and AXIN2 rs2240308 snps in mCRC pts treated with first-line FOLFIRI/BEV. More importantly, This is first time confirmed that this predictive value is dependent on gender and tumor location in over 900 mCRC pts, suggesting Wnt signaling may play different role in female vs male and in right vs left side tumors.