According to UGT1A1 genotype, grade 4 neutropenia and febrile neutropenia occurred in 46.2 and 25.6 %, respectively, of patients with UGT1A1 *1/*6 or *1/*28 single heterozygous type in the previous QUATTRO study [8]. Here, UGT1A1 is linked to Decreased total neutrophil count.