Various biomarkers are associated with response to CRT in rectal cancer, including the expression of p53,8 Ki67,9 thymidylate synthase,10 and CD133,11 as well as alterations in KRAS. 12 Furthermore, several studies have reported gene expression signatures using microarray that predict responses to CRT in rectal cancer.13,14 Such biomarkers, however, have been neither consistently reproducible among studies nor validated for use in clinical practice.15 This evidence concerns the gene TYMS and rectal cancer.