Feasibility study of irinotecan based on UGT1A1 polymorphisms for metastatic colorectal cancer: Interim report.

505 Background: Although Irinotecan prolongs survival, it causes severe diarrhea and neutropenia. Recent pharmacogenetic studies on irinotecan have revealed significant associations of UDP-glucuronosyltransferase 1A1 (UGT1A1) polymorphisms *28 and *6, the latter being specifically detected in East Asians resulting in severe toxicity. It is necessary that the dose-finding trial that decided the optimal dose according to the gene polymorphism to draw out the maximum therapeutic effect while evading the side effect. Previously, we showed UGT1A1 polymorphisms in Japanese patients (2011 ASCO-GI). Here, we present the interim report of prospective trial of the safety about FOLFIRI therapy according to each gene type of UGT1A1 for Japanese patients with advanced CRC. Methods: From 2008, 250 Japanese patients in TOKUSHIMA University were enrolled in this study. Homo group (*6/*6 and *28/*28 or a both hetero types), hetero group (It was *28 and either *6 was hetero type), and wild group (*28 and *6 were wild types) were defined. On the 30 patients with advanced CRC treated with FOLFIRI after standard chemotherapy, wild and homo groups were administered 150mg/m2 irinotecan, and homo group was 100mg/m2. The incidences of severe toxicities in each gene type of UGT1A1 and the response rate in FOLFIRI therapy were investigated. Results: In Japanese people, UGT1A1*6 polymorphisms were higher than *28 (*6 homo 3%, hetero 27% vs *28 homo 0.5%, hetero 13%). On the 30 patients with advanced CRC treated with FOLFIRI, the genotypes of UGT1A1*28 were homozygous in 1 (3%) and heterozygous in 6 (20%), *6 were homozygous in 0 and heterozygous in 8 (27%). In *6 heterozygous patients, severe toxicities (grade 3 or more) were found (38%). In *28 heterozygous patients, 1 patient (17%) showed severe toxicities. There was no decrease of irinotecan doses in each group. The number of course to PD was 7.6 (1-23). Regarding the response rate, PR, SD, PD was observed in 2 (7%), 6 (20%) and 18 patients (60%), respectively. Conclusions: In our interim report, the dosages of irinotecan based on UGT1A1 polymorphisms are safety in FOLFIRI therapy.