TPMT and cancer: Among the FDA-approved biomarkers for anti-cancer drugs, there are: cytochrome P450 2D6 (CYP2D6) for tamoxifen; rucaparib and dihydropyrimidine dehydrogenase (DPYD/DPD) for fluorouracil and capecitabine; and thiopurine S-methyltransferase (TPMT) for cisplatin, mercaptopurine, and thioguanine.