Clinical aspects of intratumoral gene therapy.

One of the major obstacles to the development of gene therapy for cancer is our inability to deliver genes to all targets within the body. Thus, effective methodology does not exist to deliver a gene intravenously with the expectation that it will selectively localize within the target tumor, will not localize in other tissues and will be expressed efficiently. While one can take advantage of tissue-specific promoters to activate the gene only in a given target tissue, only a small fraction of the vector will be taken up in the target tissue and expressed. Consequently, since accessible local or regional tumor masses are a major problem in many cancers, there has been a strong emphasis on clinical trials in intratumoral and peritumoral gene delivery.