By Mia M. Gaudet, PhD
Scientists have long cautioned that a family history of cancer increases your personal risk of cancer. Some genetic changes (mutations) that are found in only a few families but tremendously increase risk of cancer (e.g., BRCA1/2) have been known since the 1990s. These mutations are already used by doctors to identify high risk men and women. However, there is still much of the genetic component of cancer that is unknown. Advances in genetics and technology now allow scientists to look at common changes in the genetic code to see if these changes are related to risk of cancer.
Researchers are trying to answer these questions. Recently, an international group of cancer investigators linked 74 genetic regions to cancer. These newly identified genetic regions contain common changes in their code (called polymorphisms) that have only small effects on the risk of cancer. But when you combine many polymorphisms, that risk increases.
These new polymorphisms were found by studying the genetic make-up of more than 200,000 people. Women with and without breast cancer, women who had mutations in BRCA1 or BRCA2, women with and without ovarian cancer, and men with and without prostate cancer participated in the studies.
The researchers discovered more than 40 polymorphisms related to breast cancer risk, 4 related to estrogen receptor (ER)-negative breast cancer tumors, and 2 that are related to breast cancer associated with having a mutation in BRCA1 or BRCA2. They found 23 polymorphisms newly linked to prostate cancer, and 6 that influence risk of ovarian cancer in the general population or among women with BRCA1 mutations. With these new discoveries, there are now 76 established polymorphisms for breast cancer, 12 for ovarian cancer, and 78 for prostate cancer.
Based on statistical models, it is expected that there are at least several thousand more polymorphisms yet to be identified. When all of them are known, they might be helpful in separating people in the general population who are at high risk of certain cancers from those at low risk. People at high risk could then have more intense screening and might also consider other measures to lower cancer risk. These research findings also open new avenues for molecular biologists to explore how these changes in the genetic code start or stop the formation and growth of cancer, possibly leading to new treatments one day. However, it is still too early for someone with an average risk of cancer (no strong family history) to consider genetic testing for these common polymorphisms. Although direct-to-consumer genetic tests are available on the market, genetic testing should never be considered without the advice of a family doctor and the involvement of a genetics counselor. For most people, their genetics will play only a small role in whether they get cancer.
But we do know that not smoking and maintaining a healthy weight through good diet and physical activity could help lower your risk of prostate and ovarian (along with many other cancers), and maintaining a healthy weight, being active, and limiting alcohol could reduce your risk of breast cancer. See the American Cancer Society's guidelines for healthy living for more information.
Dr. Gaudet is director of genetic epidemiology for the American Cancer Society.