The role of UGT1A1 genotyping has been evaluated in several clinical trials, and two large meta-analyses including nearly 2000 patients confirmed that carriers of the UGT1A1 *28/*28 genotype were at a higher risk for neutropenia compared to WT *1 patients even at a low irinotecan dosage (80–145 mg/m2)[124], while carriers of the *28 allele were at risk of severe diarrhea at doses above 125 mg/m2[125]. The gene discussed is UGT1A1; the disease is neutropenia.