Minami et al. [14] reported the pharmacokinetics of irinotecan in patients with or without mutations of UGT1A1*6 or *28 in 177 cancer patients, in which the area under concentration curve ratio of SN-38 glucuronide to SN-38 decreases by 35% (from 5.55 to 3.62) in heterozygous group and by 63% (from 5.55 to 2.07) in homozygous group, as compared with the wild-type group. Here, UGT1A1 is linked to cancer.