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Table of Contents What is prevention?
General Information About Breast Cancer
Breast Cancer Prevention
Get More Information From NCI
Changes to This Summary (02/22/2008)
Questions or Comments About This Summary
About PDQ
What is prevention?
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 medicines to treat a precancerous condition or to keep cancer from starting.
Back to Top General Information About Breast Cancer
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Breast cancer is a disease in which malignant (cancer) cells
form in the tissues of the breast.
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 produce milk. The lobes, lobules, and bulbs are linked by thin tubes called
ducts. | Enlarge | | | | Anatomy of the breast, showing lymph nodes and lymph vessels. |
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.
Breast cancer is the second most common type of cancer
in American women.
Women in the United States get breast cancer more than any other
type of cancer except skin cancer. The number of new cases has increased every year
over the last 30 years. 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.
Finding and treating breast cancer early may prevent death from breast cancer. Screening tests may be used to help find breast cancer. See the PDQ summary on Screening for Breast Cancer for more information.
Back to Top Breast Cancer Prevention
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Avoiding risk factors and increasing protective factors may
help prevent breast cancer.
Most people with a certain risk factor for cancer do not
actually get the disease. Doctors cannot always explain why one person gets
cancer and another does not. Talk to your doctor or other health care professional about cancer prevention methods that might help you.
The following risk factors may increase the risk of breast cancer:
Estrogen (endogenous)
Endogenous 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.
Hormone replacement therapy/Hormone therapy
Hormones that are made outside the body, in a laboratory, are called exogenous hormones. Estrogen, progestin, or both may be given to replace the estrogen no longer produced 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) and may be given in one of the following ways:
- Combination HRT/HT is estrogen combined with progesterone or progestin. This type of HRT/HT increases the risk of developing breast cancer.
- Estrogen-only therapy may be given to women who have had a hysterectomy. It is not known if this type of HRT/HT increases the risk of breast cancer.
Exposure to Radiation
Radiation therapy to the chest for the treatment of cancers increases the risk of breast cancer, starting 10 years after treatment and lasting for a lifetime. The risk of developing 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. For example, radiation therapy used to treat Hodgkin disease by age 16, especially radiation to the chest and neck, increases the risk of breast cancer.
Radiation therapy to treat cancer in one breast does not appear
to increase the risk of developing cancer in the other breast.
For women who are at risk of breast cancer due to 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 in postmenopausal women who have not used hormone replacement therapy.
Alcohol
Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.
Inherited Risk
Women who have inherited certain changes in the BRCA1 and BRCA2 genes have a higher risk of breast cancer, and the breast cancer may develop at a younger age.
The following protective factors may decrease the risk of breast cancer:
Exercise
Exercising four or more hours a week may decrease hormone levels and help lower breast cancer risk. The effect of exercise on breast cancer risk may be greatest in premenopausal women of normal or low weight. Care should be taken to exercise safely, because exercise carries the risk of injury to bones and muscles.
Estrogen (decreased exposure)
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:
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Pregnancy: Estrogen levels are lower during pregnancy. The risk of breast cancer appears to be lower if a woman has her first full-term pregnancy before she is 20 years old.
- Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding.
- Ovarian ablation: The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries, which make estrogen. 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.
Selective estrogen receptor modulators
Selective estrogen receptor modulators (SERMs) are drugs that act like estrogen on some tissues in the body, but block the effect of estrogen on other tissues. Tamoxifen is a SERM that belongs to the family of drugs called antiestrogens. Antiestrogens block the effects of the hormone estrogen in the body. Tamoxifen lowers the risk of breast cancer in women who are at high risk for the disease. This effect lasts for several years after drug treatment is stopped.
Taking tamoxifen increases the risk of developing other serious conditions, including endometrial cancer, stroke, cataracts, and blood clots, especially in the lungs and legs. The risk of developing these conditions increases with age. Women younger than 50 years who have a high risk of breast cancer may benefit the most from taking tamoxifen. Talk with your doctor about the risks and benefits of taking this drug.
Raloxifene is another SERM that helps prevent breast cancer. In postmenopausal women with osteoporosis (decreased bone density), raloxifene lowers the risk of breast cancer for women at both high risk and low risk of developing the disease. It is not known if raloxifene would have the same effect in women who do not have osteoporosis. Like tamoxifen, raloxifene may increase the risk of blood clots, especially in the lungs and legs, but does not appear to increase the risk of endometrial cancer.
Other SERMs are being studied in clinical trials.
Aromatase inhibitors
Aromatase inhibitors lower the risk of new breast cancers in postmenopausal women with a history of breast cancer. In postmenopausal women, 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. Possible harms from taking aromatase inhibitors include osteoporosis and effects on brain function (such as talking, learning, and memory).
Prophylactic mastectomy
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 lowered in these women. However, it is very important to have a cancer risk assessment and counseling about all options for possible prevention before making this decision.
In some women, prophylactic mastectomy may cause anxiety, depression, and concerns about body image.
Prophylactic oophorectomy
Some women who have a high risk of breast cancer 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. 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 onset of symptoms of menopause, including hot flashes, trouble sleeping, anxiety, and depression. Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density. These symptoms vary greatly among women.
Fenretinide
Fenretinide is a type of vitamin A called a retinoid. When given to premenopausal women who have a history of breast cancer, fenretinide may lower the risk of forming a new breast cancer. Taken over time, fenretinide may cause night blindness and skin disorders. Women must avoid pregnancy while taking this drug because it could harm a developing fetus.
The following have been proven not to be risk factors for breast cancer or their effects on breast cancer risk are not known:
Abortion
There does not appear to be a link between abortion and breast cancer.
Oral Contraceptives
Taking oral contraceptives ("the pill") may slightly increase the risk of breast cancer in current users. This risk decreases over time. The most commonly used oral contraceptive contains estrogen.
Progestin-only contraceptives that are injected or implanted do not appear to increase the risk of breast cancer.
Environment
Studies have not proven that being exposed to certain substances in the environment (such as chemicals, metals, dust, and pollution) increases the risk of breast cancer.
Diet
Diet is being studied as a risk factor for breast cancer. It is not proven that a diet low in fat or high in fruits and vegetables will prevent breast cancer.
For more information on diet and health, see the Fruits and Veggies website.
Active and passive cigarette smoking
It has not been proven that either active cigarette smoking or passive smoking (inhaling secondhand smoke) increases the risk of developing breast cancer.
Statins
Studies have not found that taking statins (cholesterol -lowering drugs) affects the risk of breast cancer.
Cancer prevention clinical trials are used to study ways to prevent cancer.
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.
New ways to prevent breast cancer are being studied in clinical trials.
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 PDQ Cancer Clinical Trials Registry for breast cancer prevention trials that are now accepting patients.
Back to Top Get More Information From NCI
Call 1-800-4-CANCER
For more information, U.S. residents may call the National Cancer Institute's (NCI's) Cancer Information Service toll-free at 1-800-4-CANCER (1-800-422-6237) Monday through Friday from 9:00 a.m. to 4:30 p.m. Deaf and hard-of-hearing callers with TTY equipment may call 1-800-332-8615. The call is free and a trained Cancer Information Specialist is available to answer your questions.
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The NCI Web site provides online access to information on cancer, clinical trials, and other Web sites and organizations that offer support and resources for cancer patients and their families. For a quick search, use our “Best Bets” search box in the upper right hand corner of each Web page. The results that are most closely related to your search term will be listed as Best Bets at the top of the list of search results.
There are also many other places to get materials and information about cancer treatment and services. Hospitals in your area may have information about local and regional agencies that have information on finances, getting to and from treatment, receiving care at home, and dealing with problems related to cancer treatment.
Find Publications
The NCI has booklets and other materials for patients, health professionals, and the public. These publications discuss types of cancer, methods of cancer treatment, coping with cancer, and clinical trials. Some publications provide information on tests for cancer, cancer causes and prevention, cancer statistics, and NCI research activities. NCI materials on these and other topics may be ordered online or printed directly from the NCI Publications Locator. These materials can also be ordered by telephone from the Cancer Information Service toll-free at 1-800-4-CANCER (1-800-422-6237), TTY at 1-800-332-8615.
Back to Top Changes to This Summary (02/22/2008)
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.
Changes were made to this summary to match those made to the health professional version.
Back to Top Questions or Comments About This Summary
If you have questions or comments about this summary, please send them to Cancer.gov through the Web site’s Contact Form. We can respond only to email messages written in English.
Back to Top About PDQ
PDQ is a comprehensive cancer database available on NCI's Web site.
PDQ is the National Cancer Institute's (NCI's) comprehensive cancer information database. Most of the information contained in PDQ is available online at NCI's Web site. PDQ is provided as a service of the NCI. The NCI is part of the National Institutes of Health, the federal government's focal point for biomedical research.
PDQ contains cancer information summaries.
The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries are available in two versions. The health professional versions provide detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions provide current and accurate cancer information.
The PDQ cancer information summaries are developed by cancer experts and reviewed regularly.
Editorial Boards made up of experts in oncology and related specialties are responsible for writing and maintaining the cancer information summaries. The summaries are reviewed regularly and changes are made as new information becomes available. The date on each summary ("Date Last Modified") indicates the time of the most recent change.
PDQ also contains information on clinical trials.
A clinical trial is a study to answer a scientific question, such as whether a certain drug or nutrient can prevent cancer. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients and those who are at risk for cancer. During prevention clinical trials, information is collected about the effects of a new prevention method and how well it works. If a clinical trial shows that a new method is better than one currently being used, the new method may become "standard." People who are at high risk for a certain type of cancer may want to think about taking part in a clinical trial.
Listings of clinical trials are included in PDQ and are available online at NCI's Web site. Descriptions of the trials are available in health professional and patient versions. Many cancer doctors who take part in clinical trials are also listed in PDQ. For more information, call the Cancer Information Service 1-800-4-CANCER (1-800-422-6237); TTY at 1-800-332-8615.
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