Q: My mother died of breast cancer. How does that affect my chances of developing breast cancer? Can I prevent it?
A: Breast and other cancers occur with increased frequency in certain families, either because of genetics or shared exposure to cancer-causing factors in a family's environment. A woman's risk of breast cancer is at least doubled if one first-degree relative (mother or sister) has breast cancer. The risk is particularly high if the relative's breast cancer occurred before menopause, involved both breasts, or if the disease affected more than one first-degree relative or close relatives in several generations.
In recent years scientists have discovered that about 8 percent to 15 percent of all breast cancer risk is directly inherited in the form of mutated genes. Women who inherit the BRCA1 gene mutation have an 85 percent chance of developing breast cancer, as well as a significantly increased likelihood of ovarian cancer. In more than half of these women the breast cancer occurs before the age of 50. About one third of women diagnosed with breast cancer before the age of 50 carry the BRCA1 gene mutation, whereas it is present in less than 2 percent of those who develop breast cancer after the age of 70. Tests for the BRCA1 gene mutation are now offered at some large cancer centers (none in Baltimore at the present time), but only as part of research studies. General screening tests are expected within the next year or so.
Less well characterized is the mutation in the BRCA2 gene, which raises the risk of breast cancer in both men and women.
Other factors associated with increased risk include obesity, alcohol, a diet high in saturated fat and possibly the use of oral contraceptives or estrogen replacement after menopause. Although these risk factors are not firmly established, it might be prudent for women with a strong family history of breast cancer to stay slim and limit saturated fat and alcohol. Eating plenty of fruits and vegetables is a good idea for women, too, since some studies have shown that these foods contain nutrients that protect against cancer.
With your family history, you should take steps to help assure early detection should breast cancer develop. These include breast self-examination, regular examinations by your doctor and mammograms.
Keep in mind, however, that smoking-related lung cancer is now the leading cause of cancer death among women; and heart disease is far and away the most frequent cause of death in women.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.