Insufficient comprehensiveness in determining CYP2D6 * alleles and CNVs contribute to inaccurate prediction of CYP2D6 metabolic activity as demonstrated in a study re-genotyping 492 breast cancer patients using Roche’s CYP450 AmpliChip assay that demonstrated significantly improved stratification of patients into activity groups and reduced misclassifications [85]. Here, CYP2D6 is linked to breast cancer.