When someone is said to be at risk for cancer, or to have a risk factor, it means that she or he may be more susceptible to developing this disease compared with the general population. Age, for instance, is a risk factor for breast cancer — the older you become, the greater your risk of developing breast cancer. Another risk factor is a family history of the disease. Risk factors are not definite predictors of cancer, however. Studies show that some people who have every risk factor live to old age without developing cancer. Other women who have no known breast cancer risk factors develop the disease.
 
No particular health hazards are linked strongly to breast cancer in the way that smoking is linked to lung cancer or a high cholesterol level is linked to heart disease. Nevertheless, knowing you have some of the risk factors may help you be more rigorous about having regular mammograms and taking steps to reduce the risk.

 

Some risk factors are things you can’t change, such as your age or family medical history. Others are within your control, such as diet and exercise. Following are the major risk factors for breast cancer:
 
Risk factors that can’t be changed

• female sex
• aging
• family medical history
• mutations in BRCA1, BRCA2, and other genes
• atypical tissue changes in the breast
• ethnic/racial background
• first menstrual period age 12 or before
• menopause after age 55
• previous breast cancer
• previous radiation treatment

Risk factors that can be controlled  

• not having children or having children later in life
• use of postmenopausal hormone therapy
• alcohol consumption
• excess weight
• sedentary lifestyle
• smoking tobacco

Gender
Both women and men develop breast cancer, but it is more common in women. This is largely because women’s breasts undergo a complex hormonal evolution — both as women mature during their teens and early 20s, and also as they experience the hormone variations of the menstrual cycle during the menstrual years.

Age
Growing older increases a woman’s susceptibility to breast cancer. Breast cancer chiefly occurs in women who are older than 50, and it’s uncommon in women under age 35, except in cases that might have a hereditary influence. As the table Breast Cancer Risk by Age shows, a 40-year-old woman faces a 1-in-67 risk of developing breast cancer in her next 10 years. By age 60, the risk increases to 1 in 29, and by age 70, it is 1 in 24. Even if a woman lives to 80 without developing breast cancer, she is still at risk and should continue to have regular mammograms.

Family medical history
Vulnerability to breast cancer increases for any wom­an who has a close blood relative diagnosed with the disease. Having one first-degree relative (mother, sister, or daughter) with breast cancer approximately doubles a woman’s risk. Having two first-degree relatives with breast cancer multiplies her risk five times.
 
In some cases, breast cancer is the direct result of a genetic mutation. If a relative’s breast cancer developed before menopause, if it affected both breasts, or if she had ovarian as well as breast cancer, there’s a good chance her cancer reflects a mutation in the BRCA1 or BRCA2 gene, or others still to be discovered. Once your doctor assesses your risk for breast cancer you can decide whether to consider having a genetic test to see whether you carry the mutation (see The Pros and Cons of Genetic Testing). Women who inherit a mutation of BRCA1 or BRCA2 have about a 50%–85% chance of developing breast cancer by the time they are 70 years old, compared with a 7% risk among all women of developing cancer by that age.

Ethnic/racial background Not all groups of women in the United States are equally susceptible to breast cancer. White women have the highest incidence, followed by black women, Asians and Pacific Islanders, Hispanics, and Amer­ican Indians/Alaska natives. The increased early detection of breast cancer by mammography and improve­ments in treatment appear to be contributing to better survival rates. Black women, however, seem to be benefiting less than white women from such advances. Among women, blacks have the highest breast cancer death rate (36%) of all racial and ethnic groups, apparently because their cancers are diagnosed at later stages, when treatment is less effective. The death rate among white women is second highest, at 27%, followed by Hispanics at 18%, American Indians/Alaska natives at 15%; and Asians/Pacific Islanders at 12%.
 
Menstrual periods and hormone exposure
Another factor in breast cancer risk is long-term exposure to ovarian hormones, particularly the female hormones estrogen and progesterone, which are produced during the menstrual cycle. Scientists suggest that it may be abnormal, biologically speaking, for a woman’s body to be exposed to the high hormone levels of the menstrual cycle for many years. Before the mid-1900s, most women didn’t start having periods until their late teens, frequently because of poor nutrition. Then, before birth control became readily available, women often spent much of their reproductive lives either pregnant or breast-feeding, both of which change breast tissue in ways that prevent breast cells from turning cancerous. Today, most girls in developed countries begin puberty around age 10–12, have their first child at a later age than previous generations, have fewer children or no children, and may not experience menopause until their 50s. That means that today, a woman’s breast cells might be subject to the hormonal stimulation for more than 40 years — a far greater lifetime exposure than most women of past centuries experienced.
 
Although the precise roles these hormones play in a woman’s breast cancer risk are not yet known, the number of menstrual cycles she has during her lifetime appears to influence her risk of cancer. For that reason, a woman’s age at menarche (when she starts menstruating) and her age at menopause (when menstruation stops) are important in determining her risk. If menarche was early (age 12 or before) and menopause was late (after age 55), she has a slightly greater chance of developing breast cancer. This risk also exists if a woman has had no children or had her first child after age 30. On the other hand, if a woman’s ovaries are removed early and she doesn’t use hormone therapy, the risk declines. The role of estrogen and progesterone in the development of breast cancer also underlies the increased breast cancer risk associated with postmenopausal hormone therapy (see Breast Cancer and Hormone Medications).

Tissue Changes in the Breast
Certain microscopic changes in breast tissue cells removed in a biopsy are markers for an increased susceptibility to breast cancer. These changes are not malignant themselves, nor do they evolve into a malignancy, but they do indicate an increased risk. These changes include:
 
Lobular carcinoma in situ (LCIS). Despite its misleading name, LCIS is not a carcinoma (cancerous) and is not precancerous. LCIS is an irregular growth of the cells lining the wall of a lobule (a milk-producing gland of the breast) that does not penetrate the gland wall. Because LCIS is not a palpable mass and usually can’t be seen as an abnormality on a mammogram, this tissue change is usually detected through a biopsy. Today, most breast cancer specialists believe that LCIS won’t turn into an invasive cancer, but they observe that women who have it are at higher risk of developing an invasive cancer. A woman with LCIS should have a mammogram every year and an examination by a breast specialist every 6–12 months.
 
Atypical lobular hyperplasia and atypical ductal hyperplasia. These also are microscopic changes in breast tissue, in which extra cells (hyperplasia) have grown in the milk glands and look "atypical," meaning unu­sual or different from normal cells. Such hyperpla­sias are sometimes found by mammography. The Nurses’ Health Study at Harvard Medical School, which has followed 120,000 nurses since 1976, has found that women who have atypical hyperplasia (confirmed by a biopsy) have a moderately increased risk of developing breast cancer compared with women without atypical hyperplasia. The risk is highest among premenopausal women. Atypical lobular hyperplasia (ALH) is more strongly linked to the risk of pre­meno­pausal breast cancer than is atypical ductal hy­per­plasia (ADH). A woman with ADH or ALH should have an annual mammogram and a clinical breast examination once or twice a year.

Previous breast cancer
Women who have been successfully treated for breast cancer have about a 1% chance each year of developing a new, second cancer in either the other breast or in the treated breast.

Previous radiation treatment
Women who’ve had high doses of radiation to the chest before age 30 — usually for Hodgkin’s disease — have a significantly increased risk of breast cancer as adults. Radiation received after age 30, however, does not increase risk. Among women in the younger group, breast cancer is usually detected 10–15 or more years after radiation therapy. A woman who received high-dose radiation therapy should have yearly mammo­grams and breast exams beginning 10 years after the radiation treatment or beginning at age 35, which­ever comes first.

A moderate link exists between alcohol use and breast cancer risk. Pooled findings from many large studies indicate that women who have one or more alcoholic drinks a day are 40% more likely to develop breast cancer than women who don’t drink at all. The Nurses’ Health Study found that drinking as little as half a drink a day increased a woman’s breast cancer risk by 30%.  (See Alcohol and Breast Cancer Risk .)
 
Scientists still don’t know how alcohol increases breast cancer risk, but they think there are three possible mechanisms. One is that alcohol can raise the amount of estrogen in the blood, and anything that increases long-term exposure to estrogen can increase breast cancer risk. Another is that alcohol somehow makes breast cells more vulnerable to carcinogens, or cancer-causing agents, possibly by making breast cells more porous and accessible to a carcinogen or by inhibiting the body’s capacity to neutralize carcinogens. Still another possibility is that alcohol interferes with the body’s ability to use folate, a vitamin that has been linked to cancer prevention. The Nurses’ Health Study and others have found that women who drink and also take extra folate have a lower risk for breast cancer than other women who drink (see How Can You Reduce Your Risk of Breast Cancer?). Reducing alcohol consumption is one of the few steps you can take to lower your breast cancer risk.

Avoiding weight gain during your adult years can help reduce breast cancer risk. In the Nurses’ Health Study, weight gain was linked to an increase in breast cancer risk for postmenopausal women. Those wom­en who had gained more than 45 pounds since age 18 had a small increase in risk of developing breast cancer. The more weight gained, the higher the risk. For women who had gained more than 45 pounds and had never used postmenopausal hormones, the risk was double that of women who had not gained weight or used postmenopausal hormones. Hormone use tends to mask the effects of weight gain.
 
Researchers think that being overweight increases the risk of breast cancer after menopause primarily by increasing levels of estrogen. Although a woman’s ovaries stop producing estrogen after men­o­pause, fat tissue continues to produce hormones that are converted to estrogen. The more weight a woman puts on after menopause, the more estrogen her body produces — a point the Nurses’ Health Study helped confirm. The relation between hormones and breast cancer explains why the increase in risk in overweight postmenopausal women appears to be more pronounced in those who have never taken postmenopausal hormones. It is not that taking postmenopausal hormones eliminates the risk of breast cancer associated with being overweight; it’s that using hormones likely hides the effect that weight has on risk.

Sedentary lifestyle Research suggests that women who are sedentary have a higher breast cancer risk than women who are physically active. Most studies of this issue have shown that higher exercise levels lower the risk of breast cancer by an average of 30%–40%. Other factors, however, such as genetics and diet, may be influencing the outcome of these studies. The strong­est evidence for exercise lowering risk is in younger, premeno­pausal women. A routine of regular, very strenuous exercise during the reproductive years may lessen a woman’s risk of breast cancer, largely because such an exercise regimen can delay the onset of menstruation, lengthen the time between periods, or decrease the number of menstrual cycles, thus reducing her exposure to estrogen. Another way that physical activity might protect against breast cancer is by bolstering the immune system.
 
Does this mean regular exercise can lower your risk of breast cancer? Although the link between exercise and a lower risk of breast cancer remains inconclusive, experts believe that the benefits of exercise in controlling weight gain (which increases risk) and other indirect evidence is sufficient to recommend regular exercise as a preventive measure.

Links between breast cancer and environmental toxic exposures have not been firmly established. Chemicals known as organochlorines, often found in pesticides including the banned substance DDT, have been studied as a possible cause of breast cancer, but studies have not confirmed this relationship. In fact, the large-scale Nurses’ Health Study found no link between breast cancer and either DDT or PCB, another organochlorine.

However, smoking for many years may increase the risk of breast cancer. A study published in the International Journal of Cancer in 2002 found that the risk of breast cancer was 60% higher among women who had smoked for 40 years than among women who had never smoked. The findings were not conclusive, but given the known health risks from smoking, it makes sense to avoid tobacco.

Scientists have looked at a variety of other exposures (including passive smoking, electromagnetic fields, and silicone breast implants) but have reported no conclusive results linking any of these exposures to breast cancer. As it stands now, no firm recommendations are available regarding toxic exposure to help prevent breast cancer.

Antiperspirants Don’t Cause Breast Cancer
Women who are worried that antiperspirants might cause breast cancer can finally rest easy. A study in the Journal of the National Cancer Institute in 2002 found that neither antiperspirants nor deodorants are linked to an increased risk for breast cancer.

E-mails proclaiming that "Antiperspirant causes cancer!" have circulated for years. They claim that antiperspirants keep the body from expelling "toxins" by blocking perspiration, and go on to explain that the toxins become trapped in the lymph nodes of the armpits, where they fuel cancer. This is untrue. The function of perspiration is to cool the body, not to rid the body of toxins.

These inaccurate and alarmist e-mails aroused such concern that in 1999 the American Cancer Society dedicated a Web page to refuting the claims. In 2000, the National Cancer Institute issued a formal statement denying any scientific evidence to support the link. Still, women worried. There was no proof that antiperspirants didn’t cause breast cancer.

But data are now available from a study of 1,600 women participating in a larger study evaluating the breast cancer risk of exposure to various environmental influences. The research, conducted at the Fred Hutchinson Cancer Research Center in Seattle, indicated no relationship between breast cancer and use of either an antiperspirant or a deodorant: 25% of breast cancer patients and 30% of healthy women in the study used antiperspirants regularly; 41% of patients and 38% of healthy women used deodorants. The differences were no greater than chance.

The authors acknowledge they had to rely on the women’s memories of their deodorant and antiperspirant use, which may have been incomplete. Still, the study’s careful design gives it considerable weight and should allay women’s fears.