Association of the polymorphisms of the tandem repeat sequence in the thymidylate synthase gene with tumor stage in colon cancer.
e14688 Background: Thymidylate synthase (TS) plays an important role in colorectal carcinogenesis and response to 5FU-based chemotherapy. TS expression can be modified due to polymorphisms in the 5'-untranslated region (5’-UTR) of the gene. The aim of this study is to investigate the association between TS polymorphisms with clinicopathological characteristics of colon carcinomas. Methods: we retrospectively studied 89 individuals with high risk stage II (obstruction, T4 stage, presence of lymphovascular invasion or preoperative CEA > 5.0) and stage III patients submitted to curative intent surgery. DNA was extracted from paraffin embedded tumor tissues and sequenced. The polymorphism studied was the variation of the number of the repeated 28-bp sequences (3 or 2 repeats) of the TS gene 5’-UTR. Results: The frequency of the polymorphisms was: 2R2R in 26 cases (29.2%), 2R3R in 36 cases (40.4%), and 3R3R in 27 cases (30.3%). We did not find associations between the frequencies of these polymorphisms and age, gender, presence of lymphovascular invasion, or level of preoperative CEA. We find a significantly higher proportion of T4 tumors between the 3R3R genotype compared with the 2R2R and 2R3R genotypes (OR=2.69; 95% CI: 1.05 – 6.94; p=0.04). By the other hand, a significantly lower proportion of positive lymph nodes were found among patients with tumors presenting the 3R3R genotype, by comparing with the 2R2R and 2R3R subgroup (OR: 0.28; 95%CI: 0.10 – 0.72; p=0.01). Five-year disease free survival and overall survival were, respectively, 81% and 85% among patients with tumors presenting the 3R3R genotype, and 62% and 67% among patients with tumors presenting 2R2R or 2R3R genotypes. These differences were not statistically significant. Conclusions: in this sample, the TS polymorphic tumor genotype 3R3R was associated with lower risk of lymph node metastases in colon carcinomas.