CYP2D6 and cancer: For the anti-cancer drugs, no PGx variants were identified in DYPD, which is relevant to 5-fluorouracil and capecitabine (CPIC Level A, FDA Tier 1), but CYP2D6 variants associated with clinically relevant phenotypes were predicted for approximately half of those patients (51%) prescribed tamoxifen (CPIC Level A, FDA Tier 3).