Breast Cancer Prevention

Older age

Besides being a woman, older age is the main risk factor for breast cancer. The chance of getting breast cancer increases as a woman gets older. A 30-year-old woman has about a 1 in 200 chance of being diagnosed with breast cancer in the next 10 years, while a 70-year-old woman has a 1 in 25 chance.

Women aged 50 to 69 years who have screening mammograms have a lower chance of dying from breast cancer than women who do not have screening mammograms. Screening by mammography decreases breast cancer mortality by identifying cases for treatment at an earlier stage.

A personal history of breast cancer or benign (noncancer) breast disease

Women with any of the following have an increased risk of breast cancer:

• A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
• A personal history of benign (noncancer) breast disease.

Inherited risk of breast cancer

Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.

Women who have inherited changes in the BRCA1 and BRCA2 genes or in certain other genes have a higher risk of breast cancer. The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.

Dense breast tissue

Having breast tissue that is dense on a mammogram is a factor in breast cancer risk. The level of risk depends on how dense the breast tissue is. Women with very dense breasts have a higher risk of breast cancer than women with low breast density.

Increased breast density is often an inherited trait, but it may also occur in women who have not had children, have a first pregnancy late in life, take postmenopausal hormones, or drink alcohol. For more information, see Dense Breasts: Answers to Commonly Asked Questions.

Reproductive history resulting in greater exposure to estrogen

Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.

The following factors in a woman's reproductive history increase the length of time her breast tissue is exposed to estrogen and may increase the risk of breast cancer:

• Early menstruation: Beginning to have menstrual periods before age 12 increases the number of years the breast tissue is exposed to estrogen.
• Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
• Older age at birth of first child or never having given birth: Pregnancy lowers a woman’s lifetime number of menstrual cycles. Breast tissue is exposed to more estrogen for longer periods of time in women who become pregnant for the first time after age 35 or who never become pregnant.

Taking hormone therapy for symptoms of menopause

Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Estrogen therapy that began close to the time of menopause is associated with an increased risk of developing breast cancer. Estrogen therapy that began at or after menopause is associated with an increased risk of developing endometrial cancer and total cardiovascular disease, especially stroke. The risk of breast cancer does not decrease after women stop taking estrogen. Combination HT is estrogen combined with progestin. This type of MHT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.

Radiation therapy to the breast or chest

Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given. The risk is highest if radiation treatment was used during puberty, when breasts are forming.

Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.

For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.

Obesity

Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.

Drinking alcohol

Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.

Reproductive history resulting in less exposure to estrogen

A woman’s reproductive history can affect the length of time her breast tissue is exposed to estrogen. Early onset of menstruation, late onset of menopause, later age at first pregnancy, and never having given birth have been linked to an increase in estrogen exposure and breast cancer risk. The following reproductive factors decrease the length of time a woman's breast tissue is exposed to estrogen and may help prevent breast cancer:

• Early pregnancy: Estrogen levels are lower during pregnancy. In one study, women who had a full-term pregnancy before age 20 had a lower risk of breast cancer than women who did not have children or who gave birth to their first child after age 35.
• Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding. Women who breastfed have a lower risk of breast cancer than women who have had children but did not breastfeed.

Taking selective estrogen receptor modulators or aromatase inhibitors and inactivators

Risk-reducing or prophylactic mastectomy

Some women who have a high risk of breast cancer may choose to have a risk-reducing or prophylactic mastectomy (the removal of one or both breasts when there are no signs of cancer). After surgery, the risk of breast cancer becomes much lower in these women and most feel less anxious about their risk of breast cancer. Some women diagnosed with breast cancer may decide to have a healthy breast removed at the same time the breast with cancer is removed. This is called contralateral prophylactic mastectomy. However, it is very important to have a cancer risk assessment and counseling about the different ways to prevent breast cancer before making any decision about surgery.

Ovarian ablation

The ovaries make most of the estrogen that is made by the body. Treatments that stop or lower the amount of estrogen made by the ovaries include surgery to remove the ovaries, radiation therapy, or taking certain drugs. This is called ovarian ablation.

Premenopausal women who have a high risk of breast cancer due to certain changes in the BRCA1 and BRCA2 genes may choose to have a risk-reducing oophorectomy (the removal of both ovaries when there are no signs of cancer). This decreases the amount of estrogen made by the body and lowers the risk of breast cancer. Risk-reducing oophorectomy also lowers the risk of breast cancer in average-risk premenopausal women and in women with an increased risk of breast cancer due to radiation to the chest. However, it is very important to have a cancer risk assessment and counseling before making this decision. The sudden drop in estrogen levels may cause the symptoms of menopause to begin. These include hot flashes, trouble sleeping, anxiety, and depression. Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density.

Getting enough exercise

Women who take part in physical exercise have a lower risk of breast cancer.

Hormonal contraceptives

Hormonal contraceptives contain estrogen or estrogen and progestin. Some studies have shown that women who are current or recent users of hormonal contraceptives may have a slight increase in breast cancer risk. Other studies have not shown an increased risk of breast cancer in women using hormonal contraceptives.

In one study, the risk of breast cancer slightly increased the longer a woman used hormonal contraceptives. Another study showed that the slight increase in breast cancer risk decreased over time when women stopped using hormonal contraceptives.

More studies are needed to know whether hormonal contraceptives affect a woman's risk of breast cancer.

Chemicals in the environment

Scientists are studying whether exposure to chemicals in the environment may increase a woman's risk of breast cancer. Studies of this kind can be difficult to conduct and interpret for many reasons:

• It is hard to determine the specific chemicals people have been exposed to in the past. It can take decades after a potential exposure before cancer develops, and a person may not be aware of or remember the past exposure.
• Even if a chemical is shown in a laboratory test to cause cancer, this does not necessarily mean it will cause cancer in people exposed to that chemical in the environment. A chemical may cause cancer when tested at high levels in laboratory studies but not at the lower levels seen in the environment.
• Individual chemicals are likely to cause only a small increase in risk, and it can be difficult to detect that increase in the context of the other factors that may influence a woman's risk of breast cancer.

These reasons make it hard to know which chemicals, if any, may increase the risk of breast cancer. More studies are needed to know whether chemicals in the environment affect a woman's risk of breast cancer. For more information, see Environmental Carcinogens and Cancer Risk.

The following have little or no effect on the risk of breast cancer:

• Having an abortion.
• Making diet changes such as eating less fat or more fruits and vegetables.
• Taking vitamins, including fenretinide (a type of vitamin A).
• Cigarette smoking, both active and passive (inhaling secondhand smoke).
• Using underarm deodorant or antiperspirant.
• Taking statins (cholesterol-lowering drugs).
• Taking bisphosphonates (drugs used to treat osteoporosis and hypercalcemia) by mouth or by intravenous infusion.
• Changes in your circadian rhythm (physical, mental, and behavioral changes that are mainly affected by darkness and light in 24 hour cycles), which may be affected by working night shifts or the amount of light in your bedroom at night.