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Genetic testing is a process which involves examining individuals' genetic material for the presence of a change that indicates why they may have developed a disease or disorder. Genetic testing may also tell patients if they are at increased risk for developing a disease such as cancer in the future, but currently do not have any symptoms of that particular disease.
Genetic testing is usually done by taking a sample of a person's blood. The changes in the genetic material that can be detected by this testing vary in size. Sometimes parts or even entire chromosomes may be altered or missing completely. Other times, a mutation is present on a gene that causes it to malfunction. One type of mutation is known as a hereditary mutation. Hereditary mutations may also be called germline mutations because they are found in all the cells of a person's body, including the reproductive or germ cells, the sperm for a male and the egg for a female. This is why hereditary mutations can be inherited, or passed from a parent to a child. Genetic testing often looks for the presence or absence of these types of mutations in genes.
Cancer is defined as one cell that grows out of control and subsequently invades nearby cells and tissue. There are several steps involved in the process that causes a normal cell to become malignant (cancerous). It is believed that different genes play a role in this specialized process. Oncogenes typically promote or encourage cell growth. However, if they are overexpressed or mutated, they may cause cancer to arise. Tumor-suppressor genes, when working properly, prevent cells from growing too quickly or out of control. They are often compared to brakes in a car. If these genes cannot perform their function because of the presence of a mutation, cells may grow out of control and become cancerous. Finally, cancer may also be caused by faulty DNA repair genes. These genes usually correct the common mistakes that are made by the body as the DNA copies itself, a normally occurring process. However, if these genes can't correct mistakes, the mistakes may accumulate and lead to cancer.
It is very important to remember that while all cancer is genetic, or caused by changes in genes, just a small amount of cancer is hereditary, or passed from parent to child. It is thought that only about 5-10% of cancer falls into this category. Therefore, the majority of cancer is not hereditary. Most cancer is due to other causes, such as environmental exposures. Usually it is very difficult to determine the exact cause of cancer that is not known to be the result of an altered gene.
Author Info: Tiffani A DeMarco M.S., The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Cancer, 2002
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