Breast Cancer Prevention (PDQ®)
Topics in This Section
- What is prevention?
- General Information About Breast Cancer
- Breast Cancer Prevention
- Changes to This Summary (10/09/2014)
- About This PDQ Summary
- About PDQ
- Purpose of This Summary
- Reviewers and Updates
- Clinical Trial Information
- Permission to Use This Summary
- Contact Us
- Questions or Comments About This Summary
- Get More Information From NCI
Cancer prevention is action taken to lower the chance of getting cancer. By preventing cancer, the number of new cases of cancer in a group or population is lowered. Hopefully, this will lower the number of deaths caused by cancer.
To prevent new cancers from starting, scientists look at risk factors and protective factors. Anything that increases your chance of developing cancer is called a cancer risk factor; anything that decreases your chance of developing cancer is called a cancer protective factor.
Some risk factors for cancer can be avoided, but many cannot. For example, both smoking and inheriting certain genes are risk factors for some types of cancer, but only smoking can be avoided. Regular exercise and a healthy diet may be protective factors for some types of cancer. Avoiding risk factors and increasing protective factors may lower your risk but it does not mean that you will not get cancer.
Different ways to prevent cancer are being studied, including:
- Changing lifestyle or eating habits.
- Avoiding things known to cause cancer.
- Taking medicine to treat a precancerous condition or to keep cancer from starting.
The breast is made up of lobes and ducts. Each breast has 15 to 20 sections called lobes, which have many smaller sections called lobules. Lobules end in dozens of tiny bulbs that can make milk. The lobes, lobules, and bulbs are linked by thin tubes called ducts.
Each breast also has blood vessels and lymph vessels. The lymph vessels carry an almost colorless fluid called lymph. Lymph vessels lead to organs called lymph nodes. Lymph nodes are small bean-shaped structures that are found throughout the body. They filter lymph and store white blood cells that help fight infection and disease. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the chest.
See the following PDQ summaries for more information about breast cancer:
- Breast Cancer Screening
- Breast Cancer Treatment
- Breast Cancer Treatment and Pregnancy
- Male Breast Cancer Treatment
- Genetics of Breast and Ovarian Cancer
Women in the United States get breast cancer more than any other type of cancer except skin cancer. The number of new cases of breast cancer has stayed about the same since 2003. Breast cancer is second to lung cancer as a cause of cancer death in American women. However, deaths from breast cancer have decreased a little bit every year for the past several years. Breast cancer also occurs in men, but the number of new cases is small.
White women have a slightly increased risk of breast cancer compared to other races.
Avoiding cancer risk factors may help prevent certain cancers. Risk factors include smoking, being overweight, and not getting enough exercise. Increasing protective factors such as quitting smoking, eating a healthy diet, and exercising may also help prevent some cancers. Talk to your doctor or other health care professional about how you might lower your risk of cancer.
NCI's Breast Cancer Risk Assessment Tool uses a woman's risk factors to estimate her risk for breast cancer during the next five years and up to age 90. This online tool is meant to be used by a health care provider. For more information on breast cancer risk, call 1-800-4-CANCER.
Being female and older age are the main risk factors for breast cancer. The risk of breast cancer in a 70 year old woman is about 10 times that of a 30 year old woman.
Over her lifetime, a woman's risk of developing breast cancer is about one hundred times a man's risk.
Women with any of the following have an increased risk of breast cancer:
- A personal history of breast cancer, ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS).
- A personal history of benign (noncancer) breast disease.
- A family history of breast cancer in a first-degree relative (mother, sister, or daughter).
Women who have inheritedcertain changes in the BRCA1 and BRCA2 genes have a higher risk of breast cancer, ovarian cancer and maybe colon 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. Men who have inherited certain changes in the BRCA2 gene have a higher risk of breast, prostate, and pancreatic cancers, and lymphoma.
Breast density 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.
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.
A woman's exposure to estrogen is increased in the following ways:
- Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
- Late menopause: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
- Late pregnancy or never being pregnant: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.
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). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT 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 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 increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.
Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.
Decreasing the length of time a woman's breast tissue is exposed to estrogen may help prevent breast cancer. Exposure to estrogen is reduced in the following ways:
- Early pregnancy: Estrogen levels are lower during pregnancy. Women who have a full-term pregnancy before age 20 have a lower risk of breast cancer than women who have not had children or who give 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.
- Ovarian ablation: The ovaries make estrogen. The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries. Also, drugs may be taken to lower the amount of estrogen made by the ovaries.
- Late menstruation: Beginning to have menstrual periods at age 14 or older decreases the number of years the breast tissue is exposed to estrogen.
- Early menopause: The fewer years a woman menstruates, the shorter the time her breast tissue is exposed to estrogen.
Women who exercise four or more hours a week have a lower risk of breast cancer. The effect of exercise on breast cancer risk may be greatest in premenopausal women who have normal or low body weight.
Hormone therapy with estrogen only may be given to women who have had a hysterectomy. In these women, estrogen-only therapy after menopause may decrease the risk of breast cancer. There is an increased risk of stroke and heart and blood vessel disease in postmenopausal women who take estrogen after a hysterectomy.
Tamoxifen and raloxifene belong to the family of drugs called selective estrogen receptor modulators (SERMs). SERMs act like estrogen on some tissues in the body, but block the effect of estrogen on other tissues.
Treatment with tamoxifen or raloxifene lowers the risk of breast cancer in postmenopausal women. Tamoxifen also lowers the risk of breast cancer in high-risk premenopausal women. With either drug, the reduced risk lasts for several years after treatment is stopped. Lower rates of broken bones have been noted in patients taking raloxifene.
Taking tamoxifen increases the risk of hot flashes, endometrial cancer, stroke, cataracts, and blood clots (especially in the lungs and legs). The risk of having these problems increases with age. Women younger than 50 years who have a high risk of breast cancer may benefit the most from taking tamoxifen. The risk of having these problems decreases after tamoxifen is stopped. Talk with your doctor about the risks and benefits of taking this drug.
Taking raloxifene increases the risk of blood clots in the lungs and legs, but does not appear to increase the risk of endometrial cancer. In postmenopausal women with osteoporosis (decreased bone density), raloxifene lowers the risk of breast cancer for women who have a high or low risk of breast cancer. It is not known if raloxifene would have the same effect in women who do not have osteoporosis. Talk with your doctor about the risks and benefits of taking this drug.
Other SERMs are being studied in clinical trials.
Aromatase inhibitors (anastrozole, letrozole) and inactivators (exemestane) lower the risk of a new breast cancer in women who have a history of breast cancer. Aromatase inhibitors also decrease the risk of breast cancer in women with the following conditions:
- Postmenopausal women with a personal history of breast cancer.
- Women with no personal history of breast cancer who are 60 years and older, have a history of ductal carcinoma in situ with mastectomy, or have a high risk of breast cancer based on the Gail model tool (a tool used to estimate the risk of breast cancer).
In women with an increased risk of breast cancer, taking aromatase inhibitors decreases the amount of estrogen made by the body. Before menopause, estrogen is made by the ovaries and other tissues in a woman's body, including the brain, fat tissue, and skin. After menopause, the ovaries stop making estrogen, but the other tissues do not. Aromatase inhibitors block the action of an enzyme called aromatase, which is used to make all of the body's estrogen. Aromatase inactivators stop the enzyme from working.
Possible harms from taking aromatase inhibitors include muscle and joint pain, osteoporosis, hot flashes, and feeling very tired.
Some women who have a high risk of breast cancer may choose to have a prophylactic mastectomy (the removal of both breasts when there are no signs of cancer). The risk of breast cancer is much lower in these women and most feel less anxious about their risk of breast cancer. However, it is very important to have a cancer risk assessment and counseling about the different ways to prevent breast cancer before making this decision.
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 prophylactic 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. Prophylactic oophorectomy also lowers the risk of breast cancer in normal 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.
Bisphosphonates are drugs used to treat osteoporosis and hypercalcemia and to prevent bone fractures in cancer patients. When taken by mouth or by intravenous infusion for more than 1 year they may lower the risk of breast cancer.
Taking oral contraceptives ("the pill") may slightly increase the risk of breast cancer in current users. This risk decreases over time. Some oral contraceptives contain estrogen.
Progestin-only contraceptives that are injected or implanted do not appear to increase the risk of breast cancer.
Studies have not proven that being exposed to certain substances in the environment, such as chemicals, increases the risk of breast cancer.
The following do not affect 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).
Cancer prevention clinical trials are used to study ways to lower the risk of developing certain types of cancer. Some cancer prevention trials are conducted with healthy people who have not had cancer but who have an increased risk for cancer. Other prevention trials are conducted with people who have had cancer and are trying to prevent another cancer of the same type or to lower their chance of developing a new type of cancer. Other trials are done with healthy volunteers who are not known to have any risk factors for cancer.
The purpose of some cancer prevention clinical trials is to find out whether actions people take can prevent cancer. These may include exercising more or quitting smoking or taking certain medicines, vitamins, minerals, or food supplements.
Clinical trials are taking place in many parts of the country. Information about clinical trials can be found in the Clinical Trials section of the NCI Web site. Check NCI's list of cancer clinical trials for breast cancer prevention trials that are now accepting patients.
The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.
Editorial changes were made to this summary.
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