Purpose: We investigated whether the determination of orotate phosphoribosyltransferase (OPRT) and thymidylate synthase (TYMS) polymorphisms could predict the toxicity of 5-fluorouracil (5-FU) in colorectal cancer patients.
Experimental design: The determination of OPRT and TYMS genotypes were done in genomic DNA extracted from blood by PCR amplification in 69 patients treated with bolus 5-FU as adjuvant chemotherapy. Associations between these polymorphisms and toxicity were evaluated retrospectively.
Results: The Ala allele in OPRT Gly213Ala polymorphism and the two tandem repeats (2R) in TYMS promoter polymorphism were associated with grade 3 to 4 neutropenia and diarrhea. The multivariate logistic regression models revealed that only TYMS promoter polymorphism had an independent value to predict grade 3 to 4 neutropenia [odds ratio, 19.2 for patients with the 2R allele compared with patients with homozygous with the three repeat (3R) alleles], whereas both OPRT and TYMS promoter polymorphisms were independent predictive factors for grade 3 to 4 diarrhea (odds ratio, 13.3 for patients with the Ala allele compared with patients in the Gly/Gly genotype and 11.1 for patients with the 2R allele compared with patients in the 3R/3R genotype). A significant difference was observed in the time to onset of severe toxicity, defined as grade 4 neutropenia and/or grade 3 to 4 gastrointestinal toxicities according to OPRT and TYMS promoter polymorphisms.
Conclusion: OPRT Gly213Ala polymorphism seems to be a useful marker for predicting toxicity to bolus 5-FU chemotherapy. Prospective translational treatment trials including larger number of patients are needed to confirm our results.