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What Causes Breast Cancer?

We do not yet know exactly what causes breast cancer, but we do know that certain risk factors are linked to the disease. A risk factor is anything that increases a person's chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, such as smoking, can be controlled. Others, like a person's age or family history, can't be changed. But having a risk factor, or even several, doesnít mean that a person will get the disease.

Some women who have one or more risk factors never get breast cancer. And most women who do get breast cancer donít have any risk factors. While all women are at risk for breast cancer, the factors listed below can increase a womanís chances of having the disease.

Risk Factors You Cannot Change

Gender: simply being a woman is the main risk for breast cancer. While men can also get the disease, it is about 100 times more common in women than in men.

Age: The chance of getting breast cancer goes up as a woman gets older. Nearly 8 out of 10 breast cancers are found in women over age 50.

Genetic risk factors: About 5% to 10% of breast cancers are linked to changes (mutations) in certain genes. The most common gene changes are those of the BRCA1 and BRCA2 genes. Women with these gene changes have up to an 80% chance of getting breast cancer during their lifetimes. Other gene changes may raise breast cancer risk as well.

Family history: Breast cancer risk is higher among women whose close blood relatives have this disease. The relatives can be from either the motherís or fatherís side of the family. Having a mother, sister, or daughter with breast cancer about doubles a womanís risk.

Personal history of breast cancer: A woman with cancer in one breast has a greater chance of getting a new cancer in the other breast or in another part of the same breast. This is different from the first cancer coming back (recurrence).

Race: White women are slightly more likely to get breast cancer than are African-American women. But African Americans are more likely to die of this cancer. This could be because their cancers are often found at a later stage. They may also have faster growing tumors. Asian, Hispanic, and American Indian women have a lower risk of getting breast cancer.

Earlier abnormal breast biopsy: Certain types of abnormal biopsy results can be linked to a slightly higher risk of breast cancer.

Earlier breast radiation: Women who have had radiation treatment to the chest area earlier in life have a greatly increased risk of breast cancer.

Menstrual periods: Women who began having periods early (before 12 years of age) or who went through the change of life (menopause) after the age of 55 have a slightly increased risk of breast cancer.

Treatment with DES: In the past, some pregnant women were given the drug DES (diethylstilbestrol) because it was thought to lower their chances of losing the baby. Recent studies have shown that these women have a slightly increased risk of getting breast cancer.

Breast Cancer Risk and Lifestyles

Not having children: Women who have had no children, or who had their first child after age 30, have a slightly higher risk of breast cancer. Being pregnant more than once and at an early age reduces breast cancer risk.

Birth control pills: It is still not clear what part birth control pills might play in breast cancer risk. Studies have found that women now using birth control pills have a slightly greater risk of breast cancer. Women who stopped using the pill more than 10 years ago do not seem to have any increased risk. Itís a good idea to discuss the risks and benefits of birth control pills with your doctor.

Hormone replacement therapy (HRT): It has become clear that long-term use (several years or more) of combined HRT (estrogens together with progesterone) may slightly increase the risk of breast cancer as well as the risk of heart disease, blood clots, and strokes. The breast cancers are also found at a more advanced stage, perhaps because HRT seems to reduce the effectiveness of mammograms. Five years after stopping HRT, the breast cancer risk appears to drop back to normal. Estrogen alone (ERT) does not seem to increase the risk of breast cancer as much, if at all.

At this time, there appear to be few strong reasons to use HRT, other than for short-term relief of menopausal symptoms. Because there are other factors to think about, you should talk with your doctor about the pros and cons of using HRT.

Breast-feeding and pregnancy: Some studies have shown that breast-feeding slightly lowers breast cancer risk, especially if the breast-feeding lasts 1Ĺ to 2 years. This could be because breast-feeding lowers a womanís total number of menstrual periods, as does pregnancy. One study found that having more children and breast-feeding longer could reduce the risk of breast cancer by half.

Alcohol: Use of alcohol is clearly linked to a slightly increased risk of getting breast cancer. Women who have 1 drink a day have a very small increased risk. Those who have 2 to 5 drinks daily have about 1Ĺ times the risk of women who drink no alcohol. The ACS suggests limiting the amount you drink, if you drink at all.

Diet: Being overweight is linked to a higher risk of breast cancer, especially for women after change of life and if the weight gain took place during adulthood. Also, the risk seems to be higher if the extra fat is in the waist area. But the link between weight and breast cancer risk is complex, and studies of fat in the diet as it relates to breast cancer risk have often given conflicting results.

Since diet and weight have been shown to affect the risk of getting several other types of cancer as well as heart disease, the ACS says itís best to stay at a healthy weight and limit your use of red meats, especially those high in fat or processed.

Exercise: Studies show that exercise does reduce breast cancer risk. The question is: how much exercise is needed? One study found that as little as 1 hour and 15 minutes to 2 and a half hours per week of brisk walking reduced the risk by 18%. Walking 10 hours a week reduced the risk a little more.

Uncertain Risk Factors

A lot of research is being done to learn how the environment might affect breast cancer risk. At this time, research does not show a clear link between breast cancer risk and environmental pollutants, such as pesticides and PCBs.

While a direct link between smoking and breast cancer has not been found, some studies suggest it might increase breast cancer risk, particularly for women who start smoking as teens. Smoking affects your overall health and increases the risk for many other cancers, as well as heart disease. If you smoke, you should make every attempt to quit.

Internet e-mail rumors have suggested that underarm antiperspirants can cause breast cancer. There is very little evidence to support this idea. Also, there is no evidence to support the idea that underwire bras cause breast cancer.

Several studies show that induced abortions do not increase the risk of breast cancer. Also, there is no evidence to show a direct link between miscarriages and breast cancer.

Silicone breast implants can cause scar tissue to form in the breast. But several studies have found that this does not increase breast cancer risk. If you have breast implants, you might need a special x-ray picture during mammography.

A few recent studies have suggested that women who work at night (nurses on the night shift, for example) have a higher risk of breast cancer. But this has not yet been proven. Also, a recent study suggested women who took antibiotics may have a slightly higher risk of breast cancer. This link is also not clear yet.

American Cancer Society website: