Gene delivery, transfection, cytotoxicity, and many other factors influence the ability of gene therapy to treat cancer. In addition, as with pharmacologic agents, longer exposure to higher concentrations of gene products should intensify their effects (Wada et al., 2007). Cytotoxic gene products, such as FasL and TRAIL, may remain in tissues after the death of the transfected cells, and they are known to induce apoptosis in both transfected cells and neighbouring cells (Hyer et al., 2003; Kagawa et al., 2001). They have been examined for use in cancer gene therapy and its effects have been examined in vitro and in vivo (Elojeimy et al., 2006; Griffith et al., 2009). FasL delivered via a viral vector can reduce tumour size and improve prognosis in an explanted tumour model.