A Genotype-Directed Study To Optimize Dosing Of Irinotecan According To The Ugt1a1 Genotype.

2570 Background: The risk of severe neutropenia from irinotecan (I) is in part related to UGT1A1*28, a polymorphism that reduces the elimination of SN-38, the active metabolite of I. We aimed to identify the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of I in advanced solid tumor patients (pts) stratified by*1/*1, *1/*28, and *28/*28 genotypes. We hypothesized that *1/*1 pts would tolerate a higher MTD than the standard 350 mg/m2 dose and that *28/*28 pts would require dose reduction. Methods: 68 pts (30 lung, 30 gastrointestinal, 8 other cancers) received q3w, flat-dose I. Genotype frequencies were 46% (*1/*1), 41% (*1/*28), and 13% (*28/*28). Pts (66% males, median age 68 years) had 0-1 PS (only one pt had PS 2). 82% were Caucasians, 13% African Americans, and 4% Hispanics. The I starting dose was 700 mg in *1/*1 and *1/*28 pts, and 500 mg in *28/*28 pts. Pharmacokinetics was obtained at cycle 1. DLT at cycle 1 was defined as grade (G) 4 neutropenia (N) for ≥4 days, G≥3N on a treatment...