CYP3A4 and breast cancer: CYP3A4 is abundantly expressed and plays major role in metabolising 60% of the marketed drugs including chemotherapy used to treat breast cancer patients such as CPA, docetaxel, paclitaxel, etoposide, irinotecan, imatinib, lapatinib, trastuzumab emtansine and tamoxifen [18,86].