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.