BACKGROUND: Over 50% of colorectal cancer (CRC) patients develop metastases. The aim of this study was to evaluate efficacy and tolerance of first-line FOLFIRI(R) + bevacizumab (B) treatment for metastatic CRC, and to assess genetic polymorphisms as potential markers. METHODS: Adult patients with histologically-proven, non-resectable metastatic CRC and ECOG <= 2 were included. 14-day cycles consisted of bevacizumab (5 mg/kg), irinotecan (180 mg/m2), bolus FU (400 mg/m2) and leucovorin (400 mg/m2), followed by 46-hour FU infusions (2400 mg/m2). Primary endpoint was response rate according to RECIST criteria. Secondary endpoints were overall (OS) and progression-free (PFS) survivals, response duration, and toxicity. Associations between clinical data, UGT1A1, thymidylate synthase, VEGFA polymorphisms and PFS, OS and toxicity were analyzed. RESULTS: Sixty-two patients were enrolled (median age 68y). 59/62 patients were eligible and evaluable for response at 6 months: 28 showed partial response (47.5%; 95%CI; 34.3-60.9), 20 stable disease (33.9%) and 11 progression (18.6%). Grade 3/4 toxicities were as follows: neutropenia 16.1%; diarrhea 11.3%; nausea-vomiting 1.6%. Median response duration was 9.5 months (range 2.7-20); median PFS 10.3 months (range 8.8-11.7); and median OS 25.7 months (range 20.2-29.7). 11/59 initially unresectable patients were resectable after treatment. VEGFA polymorphism (rs25648) was associated with better OS (HR: 3.61; 95%CI: 1.57-8.30). CONCLUSIONS: FOLFIRI(R) + bevacizumab is active with good response rate, long median OS, and a good safety profile. A VEGFA polymorphism might have a prognostic value in this malignancy.Trial registration: Clinicaltrials.gov: NCT00467142 (registration date: April 25, 2007).