The UGT1A1*1 allele has been assigned as a normal function allele by CPIC. Patients carrying the UGT1A1*1 allele in combination with another normal function allele may have decreased likelihood of neutropenia when treated with irinotecan-based regimens as compared to patients with one or two decreased function alleles. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence irinotecan related neutropenia.