TYMS and frontotemporal dementia: [32] The 5-FU-resistant HCT116 cell line established in our study might also have a high TS expression level, and our data may support previous data reported by other groups showing that FTD induces cytotoxicity independently of the TS expression level, [17] suggesting that the DNA damage response (DDR) after the misincorporation of FTD into DNA is the main mechanism of action in FTD cytotoxicity, rather than TS inhibition.