Irinotecan (CPT-11) is now widely used as the first-line chemotherapy for mCRC. There were 4 key enzymes for CPT-11 metabolizing, CYP3A4, UDP-glucuronosyltransferase, carboxylesterase(CES), and ATP-binding cassette (ABC) transporters. Genetic variations of those enzymes may cause the heterogeneity in safety and efficacy of CPT-11. The aim of this study is to figure out the correlation between the genetic polymorphism and the drug response.