A phase I study of infusional 5-fluorouracil, leucovorin, oxaliplatin and irinotecan in Japanese patients with advanced colorectal cancer who harbor UGT1A1*1/*1,*1/*6 or *1/*28.

Objective: To evaluate the safety and efficacy of combination chemotherapy with 5-fluorouracil (5-FU), leucovorin, irinotecan and oxaliplatin (FOLFOXIRI) in Japanese patients with advanced colorectal cancer.

Methods: This phase I dose-finding study was designed to determine the maximum tolerated dose (MTD), recommended dose (RD) or both of FOLFOXIRI. Patients with UDP-glucuronosyltransferase (UGT) 1A1*6/*6, *28/*28 and *6/*28 genotypes were excluded, because these UGT1A1 genotypes are linked to severe neutropenia in Japanese.

Results: A total of 10 Japanese patients with advanced colorectal cancer were studied. The MTD of FOLFOXIRI in these Japanese patients was 165 mg/m(2) irinotecan, 85 mg/m(2) oxaliplatin and 2,400 mg/m(2) 5-FU. Accordingly, the RD of FOLFOXIRI was determined to be 150 mg/m(2) irinotecan, 85 mg/m(2) oxaliplatin and 2,400 mg/m(2) 5-FU. Toxic effects, evaluated until the completion of 4 cycles, were manageable. Grade 3-4 neutropenia occurred in 27% of cycles, but there was no febrile neutropenia. Among the 9 assessable patients, the objective response rate was 89%.

Conclusions: We thus determined the RD of FOLFOXIRI in Japanese patients with advanced colorectal cancer who do not have UGT1A1*28/*28, *6/*6 or *6/*28 genotypes. Our results indicate that FOLFOXIRI is a well-tolerated regimen for these Japanese patients.