Association of Capecitabine Pharmacokinetics and Toxicity With Aging

This is a multi-centre prospective non-interventional study designed to evaluate the effects of patient age on the pharmacokinetics of capecitabine and its metabolites 5’DFCR, 5’DFUR, and 5-FU. In addition, the study will assess the correlation between the pharmacokinetic parameters calculated and cytidine deaminase, biomarkers of aging, clinical frailty, treatment outcome, and toxicity. To be enrolled, patients must have breast or colorectal cancer and be eligible to receive capecitabine monotherapy in accordance with its approved clinical usage in the UK. Treatment will be administered according to NICE guidelines as well as the clinical judgement of the prescribing physician. One hundred patients (50 breast cancer patients, 50 colorectal cancer patients) who are about to start treatment with capecitabine monotherapy will be recruited to the study and undergo study procedures within the first week of treatment.