The current delineation of the molecular basis of cancer provides a strong rationale to consider gene therapy approaches for cancer as a complement to other cancer therapies. Phase III trials focused on adenoviral vector-mediated delivery of wild-type p53 to compliment p53 mutations were recently initiated for head and neck cancer and ovarian cancer. Clinical testing of the tumor inhibitory gene E1A, delivered by synthetic vectors is ongoing. Positive clinical data from these clinical studies will establish the use of gene therapy as a component of the multimodal treatment for certain cancers.