TYMS and rectal cancer: Nelson et al. investigated SNP located in the promoter region of the TS gene, which potentially affect the enzymatic activity and catabolism of 5-FU, in 50 rectal cancer patients and found that patients with at least one thymidylate synthase 3G allele were more likely to have a complete or partial pathologic response to nCRT containing 5-FU, with odds ratio of 10.4 (95% CI = 1.3–81.6, p = 0.01), than those without [134].