SN-38 is metabolized by uridine diphosphate-glucuronosyltransferase family 1 member A1 (UGT1A1)–mediated glucuronidation, and the risk of developing neutropenia is increased in patients homozygous for the UGT1A1*28 allele compared with heterozygous or wild-type patients [97, 103, 105, 106]. The gene discussed is UGT1A1; the disease is neutropenia.