Much of today's cancer research is devoted to finding missing or defective genes that cause cancer or increase an individual's risk for certain types of cancer. Gene research at MD Anderson has resulted in many important discoveries. We identified the mutated multiple advanced cancers gene (MMAC1) involved in some common cancers. We also performed the first successful correction of a defective tumor suppressor gene (p53) in human lung cancer. Current gene therapies are experimental, and many are still tested only on animals. There are some clinical trials involving a very small number of human subjects.
The potential benefits of gene therapy are two-fold:
- Gene-based treatments can attack existing cancer at the molecular level, eliminating the need for drugs, radiation or surgery
- Identifying cancer susceptibility genes in individuals or families can have a major role in preventing the disease before it occurs
The focus of most gene therapy research is the replacement of a missing or defective gene with a functional, healthy copy, which is delivered to target cells with a "vector." Viruses are commonly used as vectors because of their ability to penetrate a cell’s DNA. These vector viruses are inactivated so they cannot reproduce and cause disease. Gene transfer therapy can be done outside the body (ex vivo) by extracting bone marrow or blood from the patient and growing the cells in a laboratory. The corrected copy of the gene is introduced and allowed to penetrate the cells’ DNA before being injected back into the body. Gene transfers can also be done directly inside the patient’s body (in vivo).
Other therapies include:
- Injecting cancer cells with special genes that make the tumor more receptive to the effects of anti-cancer drugs
- Introducing the multi-drug resistant (MDR) gene into bone marrow to make stem cells more immune to the toxic side effects of anticancer drugs. Stem cells are responsible for the production of blood cells.
Gene therapy is a complicated area of research, and many questions remain unanswered. Some cancers are caused by more than one gene, and some vectors, if used incorrectly, can actually cause cancer or other diseases. Replacing faulty genes with working copies also brings up ethical issues that must be addressed before these therapies can be accepted for preventing cancer. Talk to your cancer specialist about the implications of gene therapy.