For example, DPWG, but not CPIC, published guidelines for irinotecan dosing according to UGT1A1 genotype, whereas among the four regulatory agencies listed in the table, only Health Canada/Santé Canada (HCSC) requires CYP2D6 genotyping prior to the prescription of tamoxifen for breast cancer. This evidence concerns the gene CYP2D6 and breast cancer.