In the safety and tolerability study of a novel FOLFIRABRAX regimen in patients with gastrointestinal cancers by Joshi and colleagues (1), the irinotecan doses were determined by UGT1A1 genotypes: 180, 135, and 90 for wild-type (*1/*1), heterozygous (*1/*28), and homozygous (*28/*28) patients, respectively. The authors reported that this regimen with genotype-guided dosing of irinotecan was tolerable based on the result that dose-limiting toxicities occurred in 5 of 23 (22%) wild-type, 1 of 19 (5%) heterozygous, and 0 of 7 homozygous patients. However, their conclusion truly concerns us that the regimen is not strong enough for patients with any of the genotypes. According to the genotype-guided dose-finding studies of irinotecan in analogous FOLFIRI regimens, the maximum-tolerated or recommended doses for wild-type and heterozygous patients were more than 300 mg/m2 and that for homozygous patients was 130 mg/m2 (2, 3)....

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