Since variants of not only UGT1A1, but also other genes, including UGT1A7, UGT1A9, ABCB1 and ABCC2, have been reported to be involved in the occurrence of CPT-11-induced severe neutropenia (6,11,21,32–35), rare variants of these genes should be investigated in the future. Here, UGT1A1 is linked to Decreased total neutrophil count.