With respect to the real prognostic impact of TS on the natural history of colorectal cancer, the few studies conducted on mainly small series of patients not treated with systemic therapy (Yamachika et al, 1998; Sanguedolce et al, 1998; van Triest et al, 2000; Takenoue et al, 2000; Edler et al, 2000, 2002) have shown inconclusive results. Here, TYMS is linked to colorectal cancer.