The liposome-mediated transfection of E2F-1 via the LipofectamineTM kit (Invitrogen Life Technologies, Carlsbad, CA) as described in Crowe et al. does not guarantee transfection of 100% of the cancer cells [7], nor do any of the adenoviral-mediated studies previously mentioned [10-12]. Here, E2F1 is linked to cancer.