This lack of response to normal signals may be due to abnormalities in how genes are expressed; meaning how they translate genetic information into building proteins and other building blocks of cells. Synthesis of normal proteins helps guide normal growth, while synthesis of abnormal proteins due to abnormal genetic messages causes abnormal growth.
Many research studies have shown that this may be due to the oversupply or too much expression of genes that cause normal cells to become cancerous. These abnormal genes are called oncogenes. In addition, genes which normally prevent mutations, called tumor-suppressor genes, may be somehow reduced in number or activity. The exact details as to how these changes come about are the subject of intense research, but both reducing oncogenes and increasing suppressor genes are the subject of so-called "targeted" anti-cancer therapy.
Either reduction of oncogene activity or restoring the number and effectiveness of tumor suppressor genes requires some type of carrier to convey the new or "fixed" genetic information to cancer cells. There are limitations to this, but these are now being overcome. Basically, gene therapy depends on the ability to insert genetic information into the receiving cancer cells, allowing the abnormal cell to incorporate the new genetic information into itself and synthesize or create the desired proteins.
One carrier that has been used is the virus. Viruses exist only for the purpose of efficient transfer of the viral genes into your cells, causing flu and other diseases. Therefore, we know that viruses are able to overcome cellular defense mechanisms and get inside you to do their job. Because of this, viruses appear as suitable transfer vehicles or carriers for gene therapy. However, this means re-engineering the viruses to do what we need and not cause disease, which is no small task.
At this time, the following are some leading research strategies for gene therapy. The first is gene-replacement therapy, which is based on re-introducing normally functioning (repaired) tumor suppressor genes like BRCA1 into cancer cells. The second is gene therapy, through which modified, more effective genes are introduced which improve the anti-tumor response of the immune system or genes that can help metabolize drugs and help improve chemotherapy effectiveness or reduce side effects.
These are both known as "somatic" strategies, which means that the cells in your own body are those being modified or re-programmed genetically as part of treatment. These strategies are now entering clinical trials in many diseases, including cancer. When searching this site, make sure you scroll down to "Type of Treatment" and specify "gene therapy". The more advanced "germ cell" gene therapy, which will modify the genes in sperm and eggs for changes that can prevent cancer in future generations, is still a future concept.
Source:
Genetics for Dummies. Wiley Publishing Inc 2005.
