UGT1A1*1/*28 and *1/*6 genotypes have no effects on the efficacy and toxicity of FOLFIRI in Japanese patients with advanced colorectal cancer

Differences in efficacy and toxicity between UDP-glucuronosyltransferase (UGT) 1A1*1/*1 and *1/*6 or *1/*28 genotypes remain unclear in Japanese patients. Patients with advanced colorectal cancer who received irinotecan combined with 5-fluorouracil plus l-leucovorin (FOLFIRI) as first-line therapy were divided into two groups: those with UGT1A1*1/*1 genotype and those with UGT1A1*1/*6 or *1/*28 genotype. Efficacy and toxicity were compared between these groups retrospectively. Forty-two patients (24 *1/*1 and 18 *1/*6 or *1/*28) were evaluated. The response rate was 48% in *1/*1 group and 56% in *1/*6 or *1/*28 group (P = 0.847). Median progression-free survival was 8.6 months in *1/*1 group and 8.5 months in *1/*6 or *1/*28 group (P = 0.888). No hematologic or non-hematologic toxic effects were clearly related to UGT1A1*1/*6 or *1/*28 during the first cycle or throughout the entire course of chemotherapy. There were no significant differences in the efficacy or toxicity of FOLFIRI between patients with UGT1A1*1/*1 genotype and those with UGT1A1*1/*6 or *1/*28 genotype. Our results suggest that patients with the latter genotypes can receive FOLFIRI at the same dose of irinotecan as those with the UGT1A1*1/*1 genotype receive.