In a previous study that assessed the role of the heterozygous variant genotype, it was reported that UGT1A1*1/*6 and *1/*28 were not involved in the occurrence of G3/4 neutropenia in Japanese patients with colorectal cancer who had been treated with CPT-11 combined with 5-fluorouracil and leucovorin (30), which is similar to the results of the present study. This evidence concerns the gene UGT1A1 and neutropenia.