Related topics: •  Breast Cancer Genetic Test •  Special Report: Breast Cancer Myths

The main risk factor for getting breast cancer is being a woman (although a small percentage of men get it, too). Unlike lung cancer, which can be traced directly to smoking, or skin cancer, which is heavily influenced by sun exposure, there are few lifestyle changes that will significantly reduce your risk of breast cancer.

"There are a lot of little things you can do that may reduce your risk somewhat," says Barbara Brenner, executive director of Breast Cancer Action, an information and advocacy group for women with the disease. But Brenner and others who've scoured the scientific literature are firm on this point: 70 percent of women who've been diagnosed with breast cancer had no known risk factors -- no family history, no genetic markers and nothing in their lifestyle to explain why they got the disease.

This much is known about how women get breast cancer:

•Only 20 to 30 percent of women who are diagnosed have a family history of the disease

•Aging is a factor. About one in eight invasive breast cancers are found in women under 45, while about two-thirds of women with breast cancer are over age 55 when they are diagnosed.

•Breast cancer is influenced by estrogen production, so women who started menstruating young (before age 12) or began menopause late (after 55) have a slightly increased chance of getting it.

•Never bearing children or having them after age 30 carries a higher risk; women who have never breastfed are also at a slightly higher risk. The most protective time to have a baby is before the age of 20.The cancer society notes that it's been observed since the 19th century that breast cancer occurs with greater frequency in nuns, perhaps because they don't get pregnant. Some researchers suspect that lesbians also may be at greater risk than heterosexual women perhaps because they are more likely to have never been pregnant.

•White women are a bit more susceptible to developing breast cancer, but African-Americans are more likely to die from it. One reason for this may have to do with access to treatment. Researchers are also looking into whether African American women may be at greater risk of developing certain types of tumors that are harder to treat.

•Taking combination hormone replacement after menopause may also lead to an increased risk of developing cancerous breast tumors, according to numerous studies. One study published in the journal Menopause showed that women who took hormone replacement therapy had three times the risk of breast cancer as women who took no hormone drugs. And a study published in the July 17, 2002 issue of the Journal of the American Medical Association said that after five years, the health risks of hormone replacement therapy (HRT) outweigh the benefits.

Known as the Women's Health Initiative, the study of women taking a combination of estrogen and progestin (synthetic progesterone) was halted three years early in May 2002, when researchers found that the women who took HRT had invasive breast cancer rates 26 percent higher than women who didn't take hormones. The women on HRT also experienced rates for stroke that were 41 percent higher and heart disease rates that were 29 percent higher than women on placebo, or dummy pills.

Since that study, research has shown that long-term use of combined HRT increases a woman’s risk of breast cancer. Five years after stopping combined therapy, however, a woman’s risk seems to drop back to normal.

ERT appears to have little impact on breast cancer risk, unless it is used for more than 10 years, at which point it may increase the risk of breast and ovarian cancer. However, estrogen replacement therapy (ERT) increases the risk of uterine cancer, so it is usually only offered to women who do not have a uterus (who have had a hysterectomy).

•Recent use of birth control pills may slightly increase the risk of breast cancer, but women who stopped using them at least 10 years earlier show no increased risk.

•One lifestyle factor that has a clear link to breast cancer in study after study is alcohol consumption. Women who drink 2 to 5 drinks a day have about one and a half times the risk of women who don’t drink. More moderate drinking appears to carry a very small increase in risk. As a result, the American Cancer Society urges women to limit alcohol to one drink a day.

•Other factors under study are diet (especially saturated fat intake), being overweight (because estrogen is stored in fat cells), smoking, and exposure to x-rays and environmental pollutants such as secondhand smoke. Asian women have much lower rates of breast cancer in their own countries, which some researchers link to a low-fat diet. American women tend to consume more fat than women in Asian countries, but science has been unable to prove a clear connection between dietary fat and breast cancer.

•A study reported in the Journal of the American Medical Association in February 2004 suggests there is a link between antibiotic use and breast cancer. Women in the study who had used antibiotics for a total of 1 to 500 days were about twice as likely to develop breast cancer than women who had never used antibiotics. Does this mean that antibiotics cause breast cancer? Researchers say there's no evidence that this is the case. Because there are so many variables to consider -- like the many reasons for taking antibiotics in the first place and the complicated ways that antibiotics affect various bodily processes -- more research is needed to understand what the link between antibiotics and breast cancer really means.

One theory is that women who take antibiotics also have weaker immune systems that may predispose them to breast cancer, researchers said. Another possibility is that antibiotics kill off bacteria in the stomach that may protect women from cancer. Researchers said the data should be used to discourage doctors from over-prescribing antibiotics, but should not discourage patients who need antibiotics for serious infections from taking them. They are encouraging further research on a possible link; in the meantime, women should not stop taking prescribed antibiotics and should discuss any concerns with their doctors.

Brenner notes that many risk factors are out of our control. Women can't influence when they started menstruating or reached menopause, and deciding whether and when to have children -- especially before age 20 -- is by no means a recommended or legitimate form of disease prevention.

Aside from having no more than one alcoholic drink daily, you might think about exercising and keeping your weight down. The less exercise you get before menopause and the more body fat you have after menopause (body fat traps and stores estrogen), the greater your chances of getting breast cancer seem to be, according to the American Cancer Society. Breast cancer organizations suggest that adopting a low-fat diet with lots of fruits and vegetables won't necessarily protect you from breast cancer, but there are plenty of other good reasons (avoiding heart disease and diabetes among them) to take that route anyway.

"All women may improve their overall health and thus perhaps minimize breast cancer risk by maintaining a healthy weight, avoiding cigarettes, limiting alcohol consumption, getting regular exercise and avoiding non-diagnostic ionizing radiation (x-rays)," wrote Dr. Victor G. Vogel in CA: A Cancer Journal for Clinicians. "Nevertheless, no lifestyle modifications have yet been proven to prevent or definitively lower the risk of breast cancer."

If you have a sister, mother or daughter who's been diagnosed with breast cancer, your chances of getting it are about doubled. (If you have two close relatives with it -- such as your two sisters or your mother and your sister -- your risk goes up fivefold.)

Inherited mutations in certain genes may also increase the likelihood of breast cancer as well as ovarian cancer. About 5 to 10 percent of cases are directly due to gene mutations. You can be tested for genetic mutations that indicate a heightened risk of breast cancer, but you'll want to talk to a genetic counselor before going through with this. Women with certain ethnic backgrounds, such as those of eastern European Jewish descent, are more likely to test positive for gene mutations. Only a small number of women have those mutations, and if you have them it doesn't mean you're sure to get the disease. Also, the test can be expensive, it may not be covered by insurance and your health insurer may raise your rates on the basis of the results.

Tamoxifen is a drug that has been used for many years for both treatment and prevention. If you are among the estimated 5 to 10 percent of American women with multiple close blood relatives who've had breast cancer, taking tamoxifen could reduce your chances of getting the disease by half. If you've already had breast cancer, taking tamoxifen for five years can also reduce your risk of a recurrence by 50 percent. It works by occupying the estrogen receptors on breast cells, so that estrogen can't get at them (the hormone causes breast cells to divide, which may create mutations that lead to cancer). On the downside, tamoxifen can produce the same symptoms as menopause -- hot flashes, depression, and vaginal dryness. It also appears to increase your risk of endometrial cancer, a rare but serious form of cancer known as uterine sarcoma, and blood clots. Doctors usually recommend taking tamoxifen for only 5 years because of the increased risks of side effects after that. A recent study, however, found that the preventative effects of tamoxifen lasted for up to 10 years, even after discontinuing treatment at 5 years.

More recently approved by the FDA to help reduce breast cancer risk in post-menoapusal women is raloxifene, a drug that's used to treat osteoporosis. Although there is less information about raloxifene because it is a newer drug, it appears to have similar effects to tamoxifen. Like tamoxifen, raloxifene offers protection against bone loss, and it may have fewer negative side effects. Studies have shown that raloxifene poses less risk of uterine cancer and blood clots than tamoxifen, but it still poses a risk. Raloxifene appears to reduce the risk of invasive breast cancers like tamoxifen does, but it may not have the same effect on non-invasive cancers. Raloxifene is only available as a breast cancer prevention medication for post-menopausal women.

Researchers are also studying newer drugs called aromatase inhibitors, which are currently used to treat advanced breast cancer or to help prevent recurrence after surgery in post-menopausal women. Aromatase inhibitors (exemestane, letrozole, and anastrozole) show promise for reducing breast cancer risk as well, but they are not yet approved for this purpose. More research is needed, and little is known about their long-term effects.

This is a complicated issue that you'll need to discuss with your doctor. Taking estrogen after menopause not only helps relieve such symptoms as hot flashes and severe depression but may also reduce your risk of a bone fracture from osteoporosis. After five years, though, according to the Women's Health Initiative, you may be at greater risk for invasive breast tumors. Your doctor can help you weigh the risks and benefits on the basis of your health and your family's medical history.

American women are four to seven times as likely to get breast cancer as women living in Asia, according to the National Cancer Institute. And when Japanese, Filipino, or Chinese women immigrate to the United States, the risk that they'll develop the disease increases steadily through the generations until it's the same as that faced by women who were born here. Lifestyle factors may account for most of the difference. Women in this country tend to be heavier, drink more alcohol, and have fewer children later in life. The potential role of environmental pollutants and pesticides in the US -- and even common household chemicals -- is also under scrutiny.

The National Cancer Institute has developed an interactive tool that can help you calculate your chances of getting breast cancer. Some factors are much more important than others, and the program weights them all accordingly (for example, having a sister with breast cancer carries more significance than having had your first child after age 30). This tool may not be entirely accurate for women outside the United States, women younger than 20, or women with known mutations in their breast-cancer genes. To use the assessment tool online, visit http://www.cancer.gov/bcrisktool/. If you have any concerns about your risk of breast cancer, it's a good idea to talk to a genetic counselor. For a referral to one in your area, call the National Society of Genetic Counselors at (312) 321-6834 (press 7) or visit their website at http://www.nsgc.org.

-- Elaine Herscher is a senior editor at Consumer Health Interactive. Ann Lane is a freelance writer based in San Francisco.

References

Last updated June 9, 2009
Copyright © 2001 Consumer Health Interactive

• If you are a woman in your 40s and older, you should have a mammogram every one or two years. Women who are at increased risk for breast cancer should consider getting them more frequently. • Check your breasts for lumps, nipple discharge, or other unusual changes every month. If you don't know how to do a self-exam, ask a doctor or nurse to show you, or check our animated guide to performing a self exam. • Maintain a healthy weight and exercise vigorously at least four days a week. This can reduce your risk of getting breast cancer, according to the American Cancer Society (ACS). • Eat plenty of fresh fruits and vegetables (five to nine servings a day if possible). This may also reduce your risk of breast cancer, although the evidence isn't as strong as it is for other types of cancer, according to the ACS. • If you've just given birth, breastfeed your child. This helps protect against breast cancer.

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