UGT1A1 and cancer: Inter-individual differences are also observed in CYP3A4 expression and activity [5, 6] but are rarely associated with any detectable polymorphisms in the CYP3A4. Additionally, UDP-glucuronosyltransferase 1A1 (UGT1A1) mutant genotypes *28 and *6 are related to poor glucuronidation activity and have been shown to act as useful indictors of adverse reactions to cancer chemotherapy with irinotecan (CPT-11) [7, 8].