A risk factor is something that increases your chances of getting a disease, but having one or more risk factors does not mean that you will necessarily get the disease. Some women with several risk factors do not get breast cancer, while most women who do get the disease have no risk factors beyond being female. Some risk factors are beyond your control; others depend on your lifestyle and are within your power to change.

Those You Cannot Control

The greatest risk for breast cancer is being female. Although men do get breast cancer, they account for only 1 percent of cases. The second greatest risk is age: the older you are, the greater your risk. About 77 percent of women with breast cancer are over 50 when diagnosed. Women in their 20s account for only 0.3 percent of breast cancer cases.

Other risks include having a first-degree relative — a mother, sister, or daughter — who has had breast cancer. Family risk may have to do with genetic inheritance, but it can also be explained by similar lifestyles among family members and an inherited predisposition to the influence of those lifestyle factors (for example, obesity and early menstruation). Another risk factor is a personal history of breast cancer: if you have had cancer in one breast, you have a threefold to fourfold increased risk of developing a new cancer in the other breast, a cancer that is not a recurrence of the first tumor.

North American and European women have a higher rate of breast cancer than do women living elsewhere, though when women from countries with lower risk move to the United States their rates of breast cancer increase. White women are at slightly higher risk than African American women, although the latter are more likely to die of the disease, probably because they have less access to health care and are diagnosed later. Asian American or Hispanic American women have lower risk. Certain ethnic groups, for example Ashkenazi Jews, are at slightly higher risk.

Lifetime exposure to estrogen is a risk factor, and women who began to menstruate early or had late menopause are at increased risk, as are women who have never had children.

Does having had a breast biopsy in the past increase breast cancer risk?

Having had a previous breast biopsy does not in itself increase cancer risk. Furthermore, if the biopsy showed only fibrocystic changes without proliferative breast disease, there is no increased risk. If the biopsy was diagnosed as proliferative breast disease without atypia, there is perhaps slightly higher risk; but if the biopsy showed hyperplasia with atypia, the risk is definitely increased.

Is there a gene for breast cancer?

In 1994 researchers identified two genes, BRCAi and BRCA2, whose mutated forms contribute to inherited breast cancer; in the future many more contributing genes will probably be discovered. Every person has two copies of the BRCAi gene in the cells of his or her body, one inherited from each parent. Usually both genes function normally, but in some people one copy carries a mistake (something like a misspelling). This alteration can occur at hundreds of different sites along the BRCAi gene, and some of these changes are associated with increased risk of developing breast or ovarian cancer, and cancers of the colon and prostate.

How do the genes for breast cancer increase risk?

It is believed that the normal forms of BRCA1 and BRCA2 help prevent cancer by producing proteins that keep cells from dividing and growing abnormally. However, if a person has inherited a mutated gene from either parent, these cancer-inhibiting proteins are less effective or produced in smaller amounts, and the chances of developing cancer increase. Women with these defective genes are at very high risk for breast or ovarian cancer, a risk as high as 85-90 percent over a lifetime.

If one of your parents has a defective BRCA1 or BRCA2 gene, there is a 50-percent chance you may inherit their defective copy. If you do, then each of your children has a 50-percent chance of inheriting it from you.

Remember that the genes do not cause breast cancer. If you have inherited a mutated form of these genes, you have an increased susceptibility to breast cancer, but you will not necessarily get it. At present it is impossible to predict the percentage of women having inherited one of these genes who will actually develop breast cancer, and it is equally impossible to assess any individual woman’s risk. The altered gene is not the sole cause of breast cancer, merely a contributing factor. Only 5-10 percent of breast cancer is believed to be inherited and of these hereditary breast cancers, altered forms of BRCA1 and BRCA2 are associated with only 40-50 percent of these cases.

How common are these genes?

It is estimated that somewhere between 0.04 and 0.2 percent of women in the general population carry the mutated form of BRCA1; the mutated form of BRCA2 is less common. The prevalence of BRCA1 and BRCA2 mutations among women of Ashkenazi Jewish descent is estimated at 1-2 percent, depending on whose statistics you accept.

How important is family history as a risk factor?

You are at increased risk for breast cancer if a first-degree relative — mother, daughter, sister, and maternal aunt (your mother’s sister) — had breast cancer. If your maternal grandmother had breast cancer, you should be especially careful about doing your monthly self-exams and getting your annual physical exam and mammogram. Some physicians do not include maternal aunt and maternal grandmother as first-degree relatives, but I believe they are worth considering. Having one of these relatives with breast cancer means that you might possibly carry a gene for the disease, though probably your risk is not so high as that of women whose mothers, daughters, or sisters had breast cancer.

Does the age at which your relatives had breast cancer make a difference in your risk level?

Some physicians believe that your risk is lower if your relative had breast cancer when she was postmenopausal or elderly, but you may still carry the gene for breast cancer even if the disease did not show up in your relative until she was older.

If your mother had breast cancer, should you have genetic testing to see whether you have inherited the gene for the disease?

Genetic testing uses a blood sample to analyze DNA and determine whether you carry the mutated form of BRCA1 or BRCA2. The test is expensive, and your insurance may well not pay for it.

There are several issues you should consider before you are tested. Genetic testing can show whether you have inherited the mutated form of BRCA1 or BRCA2, but it cannot

predict whether you will actually get breast cancer.

It is worth asking yourself what you would do if you discover that you carry one of these genes. Would you, as some women choose to do, have your breasts surgically removed preventively, so that you will not get the disease? Would you have that procedure even if you knew, as is the case, that about 5 percent of women who have both breasts removed because they have a strong family history of breast cancer still get the disease?

Privacy is another crucial issue, as with human immunodeficiency virus testing. You cannot be absolutely certain that your test results will remain private. Suppose your insurance company learns that you carry the mutated form of BRCA1. It is certainly possible, though illegal, that you will be discriminated against because of that knowledge and have difficulty getting health insurance or be forced to pay more for your coverage.

Are women who have had other forms of cancer at increased risk for breast cancer?

Women who have had breast cancer seem to be at somewhat increased risk for colon cancer. Women with inherited mutations of the BRCA1 or BRCA2 gene have an increased risk for developing cancer of the ovary.

Are daughters of women who took diethylstilbestrol (diethylstilbestrol) at increased risk for breast cancer?

No, their daughters are not at increased risk, nor are the women who took diethylstilbestrol. However, women whose mothers took diethylstilbestrol are at slightly increased risk of cervical cancer.

Those You Can Control (or Influence)

Does smoking increase the risk of breast cancer?

While no scientific study shows unequivocally that smoking increases your risk for breast cancer, there is overwhelming evidence that smoking negatively affects your immune system. Many researchers strongly believe that a healthy diet helps boost the immune system and thus helps prevent breast cancer. It makes sense to avoid smoking.

How does pregnancy protect against breast cancer?

Researchers suspect that during pregnancy breast cells differentiate into new forms, which may be more resistant to the effects of stimulation by estrogen. Researchers also believe that the different forms of estrogen produced during pregnancy, primarily estriol, may be protective.

Does breast-feeding decrease the risk of breast cancer?

Although the answer is not definitively known, one study suggests that women who breast-feed for as little as four to six months during their lifetime have as much as a 20-percent decrease in breast cancer risk. The decrease is even greater for women who breastfeed before the age of 20. Other studies find less protection or none at all. Surgeons who do numerous breast cancer operations and see many cases of the disease generally believe that breast-feeding does offer protection against breast cancer, though their evidence is based on experience and is not rigorously scientific.

Do birth control pills increase the risk of breast cancer?

No solid evidence links oral contraceptive use to increased breast cancer risk. Even women who took the high-dose birth control pills of the 1960s do not seem to have a higher risk.

Does estrogen replacement therapy increase the risk of breast cancer?

Long-term Estrogen replacement therapy use, say ten to fifteen years, may increase breast cancer risk. However, recent studies suggest that the increased risk may disappear when the Estrogen replacement therapy is stopped. The studies that do indicate an increase in risk do not show higher mortality, so the kinds of cancer associated with Estrogen replacement therapy to be among the less dangerous forms of the disease.

Does drinking alcohol increase the risk of breast cancer?

Alcohol does seem to be linked with increased risk of breast cancer, and there is evidence that alcohol increases blood estrogen levels. Women who have one alcoholic drink a day have a very small increase in risk compared to nondrinkers; those who have two to five drinks daily have about one and a half times the risk.

What is the relationship between obesity and breast cancer?

It has often been suggested that there is a link between obesity and breast cancer, especially in older, postmenopausal women. The relationship is complex, perhaps influenced by factors such as whether a woman has gained weight in later life or has been overweight since childhood. Remember that fat tissue produces estrogen, so that extra weight you are carrying around makes you a walking estrogen factory.

Are there any environmental pollutants that increase the risk of breast cancer?

Current studies do not clearly show a link between breast cancer risk and exposure to environmental pollutants such as the pesticide DDE (chemically related to DDT) or PCBs (polychlorinated biphenyls).

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