We hypothesised that the 20–30% of patients with liver-only metastatic colorectal cancer (MCRC) (Mandalà et al, 2007) may represent a favourably homogeneous and clinically relevant setting for evaluating the role of TS polymorphisms for predicting response to 5-fluorouracil-based chemotherapy. The gene discussed is TYMS; the disease is metastatic colorectal cancer.