CYP2B6 and breast cancer: Furthermore, direct administration is limited to accessible tumors, as mentioned by Braybrooke et al. (2005) in their study, CYP2B6 gene was delivered in a total of nine patients with breast cancer and three with melanoma by using human CYP2B6 commercial retroviral vector, MetXia and cyclophosphamide, which showed promising results but limited use for the treatment of systemic metastases (Braybrooke et al., 2005).