In a broad sense, all cancers are genetic because they involve changes (mutations) in the cells’ DNA. Normally the cells of the body are programmed to grow, live and die in a controlled manner. The body can also repair some tissues or DNA that is damaged. However, when cells cannot repair damaged DNA, they grow out of control and can become malignant.

Some diseases are caused by a specific mutation to a specific gene. However, most cancers do not have a direct cause-and-effect relationship with gene mutations. Most cases of cancer with gene mutations may have multiple mutations that may require other mutations or environmental conditions to become active. These mutations can be acquired or hereditary.

Acquired mutations account for most cancers. They often take years to produce cancers. Hereditary mutations are much rarer, accounting for about 5 to 10 percent of cancers. These mutations are present in all the cells at birth, and thus may lead to the development of cancer earlier in life.

Some types of cancer can occur in families with above-average frequency. However, this does not mean a hereditary mutation is involved. For example, a family may have a higher-than-normal rate of smoking, tend to eat a lot of meat, be physically inactive or live near an environmental hazard such as a toxic dump. These factors can increase the risk of cancer without genetic involvement. In many individuals, an increased rate of cancer may be a coincidence.

Genetic mutations can harm, have no effect on or even help a person’s health. The greatest genetic risk associated with cancer involves two types of genes. Oncogenes are acquired or hereditary mutations that cause normal cells to grow out of control and become cancerous. Tumor suppressor genes are normal, helpful genes that control cell division, repair damaged DNA and destroy cells that cannot be repaired. If acquired or hereditary mutations inactivate tumor suppressor genes, cancer can result.

Genetic tests are currently available to identify some oncogenes, and additional genetic tests are being developed. Genetic tests for individuals involve laboratory assessment of samples of blood or other bodily substances obtained from patients. A physician may recommend such tests if an individual has a strong family history of cancer. It is important to note that a positive test result can indicate an increased risk of cancer, not that a person definitely will develop the cancer. These tests can encourage individuals to take precautions to reduce the risk of cancer, such as:

• Getting a mammogram, prostate examination, colorectal screening or other appropriate test at an earlier age or more often than the standard recommendation for the general population.
  
  
• Making beneficial lifestyle changes to reduce the risk of cancer, such as improving diet, increasing exercise and quitting smoking.
  
  
• Taking preemptive medical action, such as surgery or chemotherapy. For example, people with an inherited condition in which there are hundreds of colon polyps often have colon surgery to prevent colorectal cancer.  Women who have a mutation of the BRCA gene may choose to have prophylactic mastectomy to prevent breast cancer.

Genetic testing can have profound psychological effects and influence family-planning decisions. Test results are hard for most patients to interpret. Experts recommend that genetic counseling accompany such assessments.

In recent years genetic research has made great progress, which is expected to accelerate. Gene therapy, the use of healthy genes to repair damaged cells, is being developed to treat cancer and other conditions. Thousands of people, the majority of them Americans, have taken part in clinical trials of gene therapy, mostly for cancer. The U.S. Food and Drug Administration (FDA) has not yet approved the sale of gene therapy products, but scientists expect that eventually such innovations will be able to help fight and prevent cancer.