Patients with the rs3918290 CT genotype and cancer who are treated with tegafur, a fluoropyrimidine, may have an increased risk of drug toxicity as compared to patients with the CC genotype. This drug-variant pair has been assigned a 鈥渘o recommendation鈥?by CPIC, as it was determined to be not clinically actionable. Other genetic and clinical factors may also influence response to fluoropyrimidine-based chemotherapy.