Relationships between promoter polymorphisms in the thymidylate synthase gene and mRNA levels in colorectal cancers

Thymidylate synthase (TS) intratumoural expression may be a prognostic marker and predict outcome of 5-fluorouracil (5-FU)-based chemotherapy in colorectal cancer patients. The TS gene promoter enhancer region contains two different polymorphisms which can influence TS mRNA transcriptional and translational efficiency: a polymorphic tandem repeat sequence (2 or 3 repeats; 2R and 3R) and a single nucleotide polymorphism (SNP), G > C, within the second repeat of the 3R alleles. We studied the relationship between tumoural TS mRNA expression levels and TS gene polymorphisms in the colonic mucosa of 48 colorectal cancer patients. The 3R/3R genotype was characterised by higher TS mRNA levels in the tumour than the 2R/2R-2R/3R genotypes (P = 0.071). Regarding the relationship with the SNP polymorphism, a statistically significant difference in TS gene expression between the 3RG/3RG genotype and 2R/2R-2R/3RC-2R/3RG genotype subset was observed (P = 0.017). No statistically significant correlation was observed between experimental data and baseline clinical-pathological characteristics as well as clinical outcome in the relatively small patient series investigated. This is the first study reporting an association between the TS intra-repeat SNP and gene expression levels in colorectal cancer patients. These results suggest that in 3R/3R patients, the G > C polymorphism may be an important factor in determining TS mRNA expression levels, and warrant further investigation of the role of TS promoter polymorphisms as predictors of sensitivity to 5-FU-based chemotherapy in larger case series.