The C allele of rs75017182 when measured on plus chromosomal strand is a marker for the Hap3B allele and is assigned decreased function by CPIC. Patients with the CG genotype and cancer who are treated with capecitabine, a fluoropyrimidine-based chemotherapy, may have an increased risk of drug toxicity as compared to patients with the GG genotype. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence risk of drug toxicity.