Following absorption, capecitabine is metabolised in a three-step metabolic process, the final step being conversion to 5-FU by thymidine phosphorylase (TP): tumour selectivity results from the significantly greater TP activity in tumour tissue compared with healthy tissue (Miwa et al, 1998; Schüller et al, 2000). The gene discussed is TYMP; the disease is neoplasm.