In the internal cohort, when only UGT1A1 genotype was used, the bootstrap-corrected c-index was 0.593 in the prediction model for severe neutropenia in the first cycle of irinotecan-based regimens (odds ratio, 1.545; P=0.0020 for heterozygous vs wild-type; odds ratio, 3.106; P<0.0001 for homozygous vs wild-type) (data not shown). Here, UGT1A1 is linked to neutropenia.