RESUMEN
Colorectal cancer (CRC) is the third most common cancer and the fourth leading cause of cancer death. 5-Fluorouracil (5-FU) is an essential component of systemic chemotherapy for CRC. Our objective was to determine the genotypic frequency of polymorphisms affecting dihydropyrimidine dehydrogenase (DPYD) and thymidylate synthetase (TYMS) genes and to correlate the genetic profile with the toxicity due to 5-FU, also considering nongenetic factors. This is a prospective study that involved 66 patients. We extracted DNA by salting out methods. We carried out the genotyping of the different polymorphisms by simple PCR for the TYMS 5'UTR and by PCR-RFLP for DPYD: 1905 + 1 G > A, 85 T > C, 496 A > G, 1679 T > G, c.483 + 18G > A and the TYMS: 5'UTR VNTR, 5'UTR G > C and 3'UTR. The study of the association of DPYD and TYMS polymorphisms with the various signs of toxicity under 5-FU revealed that the polymorphisms 496 A > G were significantly associated with hepatotoxicity: OR = 3.85 (p = 0.04). In addition, 85 T > C was significantly associated with mucositis and neurotoxicity: OR = 4.35 (p = 0.03), OR = 3.79 (p = 0.02). For TYMS, the only significant association we observed for 5'UTR with vomiting: OR = 3.34 (p = 0.04). The incidence of adverse reactions related to 5-FU appears to be influenced in patients with CRC by the identified DPYD and TYMS gene polymorphisms in the Tunisian population.