About Cancer Genetics

How cancer risk can be inherited

Researchers are just beginning to understand how cancer risk can be inherited. Normally, certain genes protect the body from cancer by controlling how cells grow and react to the body's signals. When DNA changes accumulate in several of these genes in a cell, the cell stops listening to the body and reproduces itself uncontrollably -- growing into what we call a cancer.

Some people inherit changes in a cancer-associated gene from their parents. Since the DNA of a number of genes needs to be altered for a cell to become cancerous, an alteration in just one cancer-associated gene won't cause cancer by itself. But such an inherited DNA change places people who have it "one step closer" to cancer. Their risk of certain types of cancer is higher than average.

Having an altered cancer-associated gene does not necessarily mean that a person will develop cancer. The additional changes necessary for cancer to develop may not occur. What is more, taking preventive steps can lower cancer risk.

How cancer genetics experts can help

People want to know their cancer risk for many different reasons. The most common are to:

• understand the risk of cancer for themselves or their children
• discover if inheritance played a role in the development of their cancer or a family member's cancer
• obtain information about cancer screening tests, such as mammography or colonoscopy and how often the tests should be done
• make decisions about the use of hormone replacement therapy or preventive surgery
• investigate the feasibility of genetic (DNA) testing for cancer-predisposing genes.

Genetic tests

People often assume that genetic testing – where blood or tissue samples are tested to identify DNA changes associated with disease –- is all there is to cancer genetics. Genetic tests are important tools in cancer risk assessment, but they are not the only tool and they are not for everyone.

• Limitations
  Specific DNA-based tests are available to identify genetic changes associated with certain familial cancer patterns. These tests have their limitations: A test that shows a cancer-associated DNA change in one person doesn’t necessarily mean that he or she will develop cancer. On the other hand, a person who tests negative for such changes has a normal risk and may develop cancer. People have to discuss genetic test results with their doctors to understand exactly what the results mean and what the tested individuals can do to prevent cancer to which they are genetically predisposed.
• Appropriate candidates
  Most families don’t exhibit the more common familial cancer patterns. Because of this, only 10 percent of patients are appropriate candidates for genetic tests. For the rest, a close examination of the family tree to identify in which relatives cancer has developed, is an effective way of determining cancer risk.

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