CYP2C19 and breast cancer: Multiplex testing allows clinicians to easily retrieve information about a large number of potential biomarkers; for example, Roche’s AmpliChip CYP450 Test uses approximately 240 unqiue probes to detect variants in the CYP2D6 and CYP2C19 genes, which may affect a patient’s metabolism of tamoxifen when that drug is used to treat breast cancer [72].