Mariadason and colleagues demonstrated the ability of gene profiling to predict 5FU- and irinotecan-induced apoptosis in a panel of 30 CRC cell lines [16], and, importantly, they showed how this approach predicted response more accurately than 4 previously established determinants of 5FU response: thymidylate synthase, thymidine phosphorylase, mismatch repair status and p53 mutation [16]. Here, TYMS is linked to colorectal carcinoma.