More specifically, CYP3A4 activity in the liver is responsible for the activation of tamoxifen and cyclophosphamide, whereas it transforms docetaxel into inactive hydroxylated derivatives; interestingly, high CYP3A4 levels in breast cancer biopsies can predict a poor therapeutic response to docetaxel, which suggests that also the enzyme within the tumour is involved in the inactivation of this drug53. The gene discussed is CYP3A4; the disease is breast carcinoma.