Pharmacokinetic Study of Capecitabine in Elderly Cancer Patient (≥ 75 Years)

Inclusion Criteria: * Elderly patients 75 years old or more * Life expectancy of greater then or equal to 6 months * Histologically proven metastatic breast or colorectal cancer, requiring a chemotherapy by capecitabine according to the habitual schema * Metastatic situation whatever treatment line * Previous hormonotherapy for breast cancer, prior chemotherapy (without capecitabine) in adjuvant and/or metastatic indication (colorectal or breast cancer), or radiotherapy (colorectal or breast cancer) are allowed * One or more measurable target lesion (RECIST criteria) * ADL\>4 (geriatric scales) * GSD\<12 (geriatric scales) * Laboratory values : * creatinine clearance (CrCl) \>=30 mL/min according to Cockcroft formula * Adequate bone marrow function (neutrophils count \> 1.5 x 10\^9/L, platelets \> 100 x 10\^9/L, hemoglobin \[Hb\] \> 10g/dl) * Adequate hepatic function: total bilirubin \< 1,5 x upper normal limit, aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) \< 2,5x upper normal limits (in case of liver metastases \< 5 x upper normal limits) * Alcalin phosphatases \<=2,5x ULN (\<=5 x ULN if liver metastases present). * Subjects must be willing to be followed during the course of treatment/observation and follow-up. * Signed written informed consent before first course of chemotheray Exclusion Criteria: * Age \< 75 years * known brain metastases * Concomitant oncologic treatment ongoing * History of severe or unscheduled reaction to fluoropyrimidine …