TYMS and colonic neoplasm: In addition, long-term treatment with 5FU leads to increased expression of thymidylate synthase (TS), Bcl-1, Bcl-XL and Mcl-1 as well as increased activity of deoxyuridine triphosphatase and methylation of MLH1, which are associated with 5FU resistant colon cancers (reviewed in 68).