Background: To assess the predictive value of polymorphism in nine genes, primarily thymidylate synthase (TS) and orotate phosphoribosyltransferase (OPRT), which relates to 5-fluorouracil (5-FU) metabolism, for toxicity in patients treated with oral uracil/tegafur (UFT) plus leucovorin (LV).
Patients and methods: We treated 99 patients with stage II or III colorectal carcinoma with oral UFT + LV. Germline DNA from patients was genotyped for 5-FU and folate metabolism-relating genes. CYP2A6, tegafur-activating enzyme, and uridine diphosphate-glucuronosyltransferase 1A1 genetic variation were also assessed. Toxicity was graded by the National Cancer Institute Common Toxicity Criteria, version 2.0.
Results: The multivariate logistic regression revealed that OPRT 638G>C polymorphism was associated with grade 3 diarrhea [odds ratio (OR) 19.84 for patients with the C/C homozygous type compared with patients with wild type, P = 0.014] and polymorphisms of UGT1A1 were associated with hyperbilirubinemia (OR 38.76 for homozygotes and double heterozygotes of *6 or *28 compared with wild type, P = 0.0008). No relationships were observed between TS polymorphisms and any toxicity.
Conclusions: OPRT polymorphism predicts toxicity, especially grade 3 or greater diarrhea to oral UFT + LV adjuvant chemotherapy, whereas TS does not, in our study cohort. UGT1A1 polymorphism seems to be a risk factor for hyperbilirubinemia due to UFT+LV.