The T allele of this variant is a marker for the Hap3B allele and is assigned decreased function by CPIC. Patients with the TT genotype and cancer who are treated with fluorouracil, a fluoropyrimidine-based chemotherapy, may have increased risk and increased severity of drug toxicity as compared to patients with the CC genotype. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence risk of drug toxicity.