Studies in patients with metastatic colorectal cancer showed that carriers of the TS 5′-UTR 3R (3G) and/or the TS 3′-UTR 6+ alleles had adverse clinical outcomes (Pullarkat et al, 2001; Etienne et al, 2002; Park et al, 2002; Marcuello et al, 2004; Stoehlmacher et al, 2004; Martinez-Balibrea et al, 2007); however, such an association was not always detected (Lecomte et al, 2004; Jakobsen et al, 2005; Ruzzo et al, 2007a, 2007b). Here, TYMS is linked to metastatic colorectal cancer.