CYP2A6, CYP2B6, CYP2D6, CYP3A4 and CYP3A5 involved in drug metabolism of the breast cancer prodrugs CPA, tegafur and tamoxifen (Figure 3) were expressed at various levels, but no significant differences between the PAM50 groups were observed (data not shown). The gene discussed is CYP3A4; the disease is breast cancer.