Irinotecan cytotoxicity does not necessarily depend on the UGT1A1 polymorphism but on fluoropyrimidine: a molecular case report.

We have previously demonstrated that the combined use of doxifluridine and irinotecan shows a different molecular mechanism than that of the protracted venous infusion of 5-FU and irinotecan. In this analysis, there is a suggestion that doxifluridine may enhance irinotecan and enable us to decrease the dose of irinotecan without losing the strong effect by using doxifluridine instead of 5-FU. We present a colon cancer patient with the UGT1A1 polymorphism (UGT1A1 *28) as a known high risk for irinotecan, who was treated with a combination of doxifluridine and irinotecan for peritoneal dissemination resulting in stable disease for 2 years without adverse reactions, although the patient initially developed severe adverse effects to the combination of the protracted venous infusion of 5-FU and irinotecan. Even with the same ratios of fluoropyrimidine and irinotecan combinations, replacing 5-FU with doxifluridine or capecitabine could provide new strategies to obtain not only convenience but also better efficacy and safety at the molecular level.