Angelina Jolie's decision to have a bilateral mastectomy has led to high interest in the causes of breast cancer. Jolie carries a mutation of one of two genes called BRCA1 and BRCA2, which gives her an 80 percent chance of developing breast cancer in her lifetime. These genes normally prevent breast cancer, but if they mutate and become abnormal, they no longer function, leading to a higher risk of breast cancer. Approximately 12 percent of women carry one of these genes. The mutation also increases the risk of breast cancer in men, and ovarian, pancreatic and colon cancers.

The breast cancers caused by the BRAC1 gene abnormality tend to be estrogen-receptor-negative. This means using treatments to remove estrogen are not as effective as chemotherapy. The BRAC2 gene is associated with tumors that require estrogen, so when this gene is mutated, anti-estrogen treatment is more effective.

You should be screened for these genes if many close family members, often before age 50, have had breast cancer; if there is a family history of both breast and ovarian cancers, particularly if they have occurred in one individual; if a relative has had cancer in both breasts; or if a male relative has had the disease. An abnormal gene is more likely in Ashkenazi Jews and African-Americans diagnosed with the disease at age 35 or younger.

If they're able to identify an abnormal gene early, and because of the high risk of cancer, many women are electing to have a bilateral mastectomy. These days all breast tissue can be removed, leaving behind the skin and areola. With an implant, the breasts can look perfectly normal. Doctors will advise some woman with the BRAC2 abnormality to have an oophorectomy, a surgical procedure to remove one or both of the ovaries, to reduce the risk of breast cancer by 72 percent.

For women with the BRAC2 gene, treatment with tamoxifen, which blocks the effects of estrogen on breast tissue, reduces the risk of breast cancer by 62 percent, if the disease did not occur before age 35. BRAC1 gene-positive women showed no reduction in breast cancer risk by treatment with this drug.

Deciding on a treatment plan is very personal for any woman. Certainly anti-estrogen treatment is essential for women with the BRAC2 gene abnormality. And every woman should have an annual diagnostic mammogram beginning at age 25 or 10 years before the age at which breast cancer developed in a relative. Women should consider breast exams every six months, and they should learn self-examination techniques. Anyone with the gene should visit a cancer center and consider participating in clinical trials to help reduce breast cancer risk.

Even if you do not have the gene, you should know what you can do to reduce breast cancer risk. There is a strong link between age and breast cancer. More than 75 percent of all cancers occur in women older than 50, and the number is almost twice as high after the age of 60. More than one close relative with the disease increases the risk, particularly if breast cancer developed prior to menopause. If a relative has had the disease in more than one breast, the risk of developing it increases fourfold to eightfold. Having had breast cancer increases the risk of a second breast cancer threefold to fourfold.

Breast cancer is more frequent in those who had menarche at an early age, menopause at an older age, didn't have children, or had only one child at a late age.

Hormone-replacement therapy after the menopause increases the risk. This has received much attention recently, with studies suggesting that taking estrogen and progesterone not only increases the risk of breast and uterine cancer but also increases the risk of heart attack, stroke and Alzheimer's disease. Many women, nevertheless, still elect to use this treatment to prevent menopausal symptoms. However, if you already have an increased risk of breast cancer, you should avoid hormone-replacement therapy.

A sedentary lifestyle, high-fat diet, obesity, excessive alcohol intake and certain chemicals in cosmetics are all associated with a greater risk of breast cancer.

Live a heart-healthy lifestyle, eat right, exercise, make sure you are not exposed to chemicals causing breast cancer, and have mammograms regularly so you can minimize your chances of breast cancer.

Dr. David Lipschitz is the author of the book "Breaking the Rules of Aging." To find out more about Dr. David Lipschitz and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com. More information is available at: DrDavidHealth.com.