"Cancersensor" Chemotherapy

Inclusion Criteria: * Histologically-confirmed metastatic colorectal cancer; * 0 to 3 prior chemotherapy lines; * Signed informed consent; * Good understanding of the protocol and of the follow-up; * Estimated life expectancy exceeding 3 months; * At least one measurable metastatic lesion (RECIST criteria); * Performance Status (WHO) of 0 to 2; * Good haematological, hepatic and renal functions. Exclusion Criteria: * More than 2 surgical resections of metastases from colorectal cancer; * Poor performance status (\>2); * Poor haematological, hepatic or renal functions; * Uncontrolled chronic disease; * Serious unhealed wound, ulcer or fracture within the previous month; * Clinical or laboratory finding suggesting possible abnormalities in nucleosides urinary excretion; * Pregnancy or breast-feeding during the previous month; * Transmeridian trip of more than 4 time zones within the prior 2 weeks; * Person with legal restriction to participate into clinical research, according to the current law in France.