Genetic polymorphisms of UGTs result in reduced enzyme activity and increased toxicity. UGT1A1\*28 and UGT1A1\*6 are reported to increase CPT-11-related toxicity in Asian patients. Moreover, the area under concentration curve (AUC) ratio of SN-38G to SN-38 is decreased in Asian patients having UGT1A1 \*28 or UGT1A1\*6. This implicated that the current standard dose of CPT-11 would be overdosing for homozygous UGT1A1\*28/\*28, \*6/\*6 or \*28/\*6 patients.
The study is designed to investigate the role of prospectively dose reduction of CPT-11 in toxicity, tumor response and pharmacokinetics for homozygous UGT1A1 patients, and compare these parameters to standard dose of CPT-11 for wild-type, heterozygous or homozygous UGT1A1 patients.
