An interesting case-report on two patients with metastatic colorectal cancer and Gilbert's syndrome (a chronic nonhaemolytic unconjugated hyperbilirrubinaemia caused by a reduction in the activity of UGT1A1) treated with CPT-11 provided the first clinical evidence linking deficiency in the UGT1A1 activity and irinotecan-related toxicity (Wasserman et al, 1997). Here, UGT1A1 is linked to metastatic colorectal cancer.