Gene therapy has rapidly evolved into a field that is treating not only inborn errors of metabolism, but other diseases associated with poor outcomes such as malignancy, where transient gene expression can be therapeutic. Cancer gene therapy is a novel form of treatment that exploits differences at the molecular level between normal and malignant cells. Current gene therapy approaches that are being evaluated include the use of replication competent viruses, mutation compensation strategies, improved targeting with tumor specific promoters, and the utilization of enhanced infectivity viruses. An additional aspect of gene therapy that has gained increased interest in the last several years is the utilization of single-chain antibodies (scFv). Specifically, scFv have been utilized to target molecular processes associated with carcinogenesis, as well as to improve gene transfer efficiency. We will limit our discussion to the role of scFv in targeting molecular processes associated with carcinogenesis.