Gene therapy has a particular potential application to cancer because there is a strong genetic basis to many cancers. Cancers often grow and spread because of the mutations in their genes. The cancer cell's mutations may make them invisible to the immune system so they can't be rejected or the mutations may take away the growth controls built into all cells resulting in their uncontrolled growth. Gene therapy puts genes into cancer cells to make them stimulate the immune system or to restore growth control. Another approach is to put genes into the body's white blood cells to make them effective killers of the patient's cancer cells.
Gene therapy, at the present time, is considered to be highly experimental. All gene therapy treatments are part of scientific protocols which investigate the safety and side effects of the treatment as well as its effect on the cancer. All gene therapy protocols are also highly regulated in order to protect the patient participants. This includes a special committee of the National Institute of Health called RAC (recombinant DNA advisory committee). It consists of doctors, scientists, ethicists, lawyers and lay people.
The most highly developed approach to cancer gene therapy is the use of gene-modified cancer cells as vaccines. Patient's tumors are removed, the cancer cells extracted, the genes are inserted and then the patients are immunized with their own gene-modified tumor cells. This approach works very well in animal models of gene therapy, but it is to be confirmed in human cancer.
Overall, gene therapy is a highly promising approach to cancer treatment but it experimental and unproven at the present time.