Gene therapy is a new modality of treatment in which a gene is used to modify or add new biochemical properties to a patient's target cells with therapeutics purposes. Currently, this experimental therapy is under intensive development as an alternative to treat cancer, because it is possible that this therapy may generate a higher antineoplastic activity, more tissue selectivity and less contralateral effects than conventional therapy. After a decade of preclinical and clinical assays, still there are several obstacles that impose limits to the antineoplastic efficacy of this therapy. However, with the advances in molecular biology and related fields, there is a promise to improve, expand and strength the powerful antineoplastic arsenal of gene therapy.