The T allele of this variant is a marker for the Hap3B allele and is assigned decreased function by CPIC. Patients with the CC genotype and cancer who are treated with fluorouracil, a fluoropyrimidine-based chemotherapy, may have a decreased, but not absent, risk and reduced severity of drug toxicity as compared to patients with the CT or TT genotype. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence risk of drug toxicity.