Although it was not possible to establish a new panel to improve the predictability of toxicity in this study, the analysis showed that more attention should be paid to homozygote of UGT1A1*6in the context of irinotecan-induced severe neutropenia, such as constantly monitoring the levels of neutrophile granulocytes and preventive treatment for neutropenia. Here, UGT1A1 is linked to Decreased total neutrophil count.