CYP2A6 and biliary tract cancer: However, in patients with metastatic biliary tract cancer who were given a combination therapy of oxalipatin and S-1, CYP2A6 genotype was not associated with clinical efficacy or toxicity, despite CYP2A6 genotype reduced metabolizers exhibiting higher tegafur Cmax (maximal plasma drug concentration) and AUC0–24, and lower 5-fluoruracil Cmax and AUC0–24, compared to patients without CYP2A6 reduce-of-function variants [144].