Toxicity/Benefit Ratio Optimization of Chemotherapy in Colorectal Cancer (CRC) Patients by Determination of Individual Genotypic Determinants

Inclusion Criteria: Has provided written informed consent prior to study-specific screening procedures, with the understanding that the patient has the right to withdraw from the study at any time without prejudice Ages between 18 and 85 years Histologically confirmed colorectal cancer No treatment for metastatic disease No irinotecan previously administered World Health Organization (WHO) performance status < 3 Laboratory values : neutrophils > 1.5 x 10^9/L; platelet count > 100 x 10^9/L; serum creatinine < 130µmol/L; serum bilirubin < 2 x upper limit of normal (ULN); ASAT and ALAT < 2.5 x ULN; alkaline phosphatase < 5 x ULN. At least one measurable lesion by Response Evaluation Criteria in Solid Tumors (RECIST) criteria Exclusion Criteria: History of another malignancy except cured basal cell carcinoma of the skin or carcinoma in situ of the uterine cervix, breast or bladder. Other concomitant anticancer therapy. Pregnant or lactating women. Women of childbearing potential unless using a reliable and appropriate contraceptive method. Symptomatic cerebral or leptospiral metastasis. Intestinal obstruction. Uncontrolled seizures (diabetes, severe infection). Clinically significant cardiac disease. Central nervous system disorders or severe psychiatric disability. Participation in any investigational study within 4 weeks.