After the irinotecan dose was reduced, the incidences of grade 3~4 diarrhea and grade 3~4 neutropenia were significantly decreased in both the dose reduction group and non-dose reduction group for patients with UGT1A1*28 (p = 1.000; p = 0.613) and UGT1A1*6 (p = 0.442; p = 0.139) in Table 12. The gene discussed is UGT1A1; the disease is neutropenia.