Exploring Family History of Cancer

By Mary Ahrens, M.S., C.G.C.

Only about 5 to 10 percent of cancers are caused by a single gene, or inherited. Cancers that are known to be inherited in some families include breast, ovarian, prostate, and colon. It is often unclear whether a pattern of cancer in a family is caused by a single gene or may be a combination of genes and other risk factors such as smoking, having a diet high in fat, and excess sunburn; or just a matter of chance.

The discovery of cancer genes has significantly improved our understanding of how cancer can be inherited. For instance, abnormalities (mutations) in certain inherited genes have been found to lead to some colon cancers. Additionally, two breast cancer genes, BRCA1 and BRCA2, were discovered in recent years. These genes can also be inherited and have been shown to greatly increase a person's risk for developing breast cancer and/or ovarian cancer.

Researchers have developed certain genetic tests that detect known cancer-related genes in the body. These tests identify individuals who are at increased risk of getting cancer. Genetic testing for cancer is not intended for the general public, but it can be useful for some individuals with a significant family history of cancer. For example, a person with a family history of breast cancer who is found to have a BRCA1 or BRCA2 gene mutation may benefit from frequent screenings, or surgery to remove the breasts or ovaries. Though these measures may significantly lower a person's risk, they are not a guarantee that the person will remain cancer-free. The goal of genetic testing is to make people aware of their increased risk of cancer and give them options for early detection and possibly prevention of cancer.

To determine if your family has a history of cancer, ask yourself if you or several relatives have had cancer, if you or your relatives were diagnosed under the age of 50, had more than one type of cancer, or had a rare or unusual cancer. If you answer yes to one or more of these questions, you might consider a genetic evaluation and genetic testing. However, while genetic testing can identify known cancer genes, many other factors can influence a person's risk of actually developing cancer. Even people who do not have a cancer gene may still be at risk for a particular type of cancer based on their family history.

If you are concerned about your family history of cancer or have questions about genetic testing for cancer, it is important to meet with a genetic counselor, a specially trained professional who can assess your family's history of cancer and recommend ways to use that information. It is important that you carefully weigh the risks as well as the benefits of genetic testing. If you choose to undergo testing, a genetic counselor also can help you and your loved ones interpret the results of the tests and talk with you about possible prevention and treatment measures.