Abstract
Background: To evaluate a new UGT1A and DPYD polymorphism panel to better predict irinotecan-induced toxicity and the clinical response in Chinese patients with metastatic colorectal cancer (mCRC). Methods: The genotypes of UGT1A (UGT1A1*6, UGT1A1*27, UGT1A1*28, UGT1A7*2, UGT1A7*3, UGT1A7*4 and UGT1A9*22) and DPYD (DPYD*5, DPYD c.1896 T > C, and DPYD*2A) were examined by direct sequencing in 661 mCRC patients receiving irinotecan-based chemotherapy. The influences of UGT1A and DPYD polymorphisms on severe irinotecan-induced toxicities and clinical outcomes were assessed. Results: In the cohort studied here, the incidence of UGT1A1*6, UGT1A1*28, UGT1A7*2, UGT1A7*3, UGT1A9*22, DPYD*5, and DPYD c.1896 T > C variants were 34.8%, 24.2%, 34.3%, 39.4%, 81.8%, 48.4% and 20.4%, respectively. UGT1A1*27 and DPYD*2A had low frequencies and UGT1A7*4 was not found. A total of 59 patients (8.9%) suffered severe diarrhea and 136 patients (20.6%) suffered severe neutropenia. UGT1A1*28 heterozygotes (OR = 2.263, 95%CI 1.395-3.670), UGT1A1*28 homozygotes (OR = 5.910, 95%CI 1.138-30.672) and UGT1A1*6 homozygotes (OR = 4.737, 95%CI 1.946-11.533) were independent risk factors for severe neutropenia. UGT1A polymorphisms were not found to relate to severe diarrhea. DPYD*5 was determined to be an independent risk factor for severe diarrhea (OR = 2.143, 95%CI 1.136-4.041). Neither DPYD*5 nor DPYD c.1896 T > C was found to relate to severe neutropenia. In the first-line irinotecan-based treatment, UGT1A1*28 and DPYD*5 contributed to higher response rates (P = 0.043 and P = 0.019, respectively), while DPYD*5 was found to associate with better progression-free survival (P = 0.015). UGT1A1*27 contributed to worse overall survival (P < 0.001). Conclusion: Results still showed UGT1A1*6 and UGT1A1*28 to be partially associated with irinotecan-induced toxicity and clinical response. An examination of more UGT1A loci, except for UGT1A1*6 and UGT1A1*28, was not helpful to improve the predictive value of irinotecan-based toxicity and efficacy. An examination of DPYD*5 assisted in the prediction of severe diarrhea.