Background: Cetuximab and chemotherapy as first-line therapy for patients with KRAS wild type prolong survival. However, COIN trial has not demonstrated the survival benefit of FOLFOX or XELOX and cetuximab therapy. Few data are available on its benefit for patients with KRAS and BRAF wild-type. Methods: The aim of this study was to assess the efficacy of first-line FOLFOX or bi-weekly XELOX and bi-weekly cetuximab in KRAS/BRAF wt mCRC. Chemonaive patients received FOLFOX or biweekly XELOX (oxaliplatin 85 mg/ m²/day 1 plus capecitabine 2000/m²/days 1-7) and biweekly cetuximab 500mg m²/ day 1 every 2 weeks. Primary endpoint was response rate(RR), other secondary endpoints were PFS, OS, DCR, safety, DI and resection rate. KRAS test (codon12,13) and BRAF test (V600E) by direct sequence were performed in Yamaguchi University. Patients with KRAS/BRAF wt were enrolled in this study. The regimen of FOLFOX or XELOX were selected by investigator’s preference, not randomized. Results: From April 2010 to May 2011, 139 pts were preregistered. KRAS and BRAF were examined from paraffin-embedded sample. 70 (50.3%) pts were KRAS/BRAF wt, and 62 pts were enrolled: The main characteristics of the entered pts were: sex (M/F) 34/28, median age 66 yrs (range 34-83 yrs). Grade 3/4 adverse events were leucopenia 4.8%, neutropenia 25.8%, skin toxity (paronychia/fissure) 9.7%, and acne 9.7%. Two CR (3.2%) and 40 PR (64.5%), 15 SD (24.2%) and 3 PD (4.8%) 2NE were observed, with an overall response rate of 67.7% and a disease control rate (CR+PR+SD) of 91.9%. The RR of FOLFOX or XELOX were 64.9% (24/37) and 72.0% (18/25), DCR were 89.2% and 96% respectively. Conclusions: FLEET was the first multicenter phase II study with prospective KRAS/BRAF analysis as a predictive biomarker for cetuximab in first-line mCRC in Japan. Results of this study indicate that both biweekly combination regimens are feasible, tolerable, and clinically active. Biweekly XELOX+cetuximab study (FLEET2) is ongoing. Clinical trial information: UMIN000003253.