We have previously demonstrated that levels of the 5‐fluorodeoxyuridylate (FdUMP) covalent complex with thymidylate synthase (FdUMP‐TS) and free‐TS (native enzyme) are higher in 5‐FU‐resistant CRC cells than in the parental cell line (HCT116). Here, TYMS is linked to colorectal carcinoma.