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Prevention of Breast Cancer
Summary Type: Prevention
Summary Audience: Patients
Summary Language: English
Summary Description: Expert-reviewed information summary about factors that may increase the risk of developing breast cancer and about research aimed at the prevention of this disease.
Prevention of Breast Cancer
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.
General Information About Breast Cancer
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. 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.
Breast Cancer Prevention
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.
Estrogen (exogenous)
Estrogen that is made outside the body, in a laboratory, is called exogenous estrogen. Taking exogenous estrogen together with progesterone increases the risk of breast cancer. Exogenous estrogen may be taken in the following ways:
X-rays
Radiation can cause breast cancer. Treatment with radiation during childhood seems to increase breast
cancer risk more than treatment as an adult. For example, radiation used to treat Hodgkin's 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.
Obesity
Obesity increases
the risk of breast cancer in postmenopausal women.
Alcohol
Drinking alcohol may increase the risk of breast cancer.
Genetics
Women who have inherited certain mutations in the BRCA1 and BRCA2 genes have a higher risk of breast cancer. BRCA1 and BRCA2 are tumor suppressor genes . If these genes have a mutation and don't work as they should, the risk of breast cancer is increased. Research is being done to identify other high-risk genes.
The following protective
factors may decrease the risk of breast cancer:
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:
-
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.
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
In postmenopausal women, aromatase inhibitors decrease the body's estrogen and lower the risk of breast cancer. After menopause, most of a woman's estrogen is not made by the ovaries. It comes from another hormone, called androgen . Aromatase inhibitors stop an enzyme called aromatase from turning androgen into estrogen. Possible harms from taking aromatase inhibitors include osteoporosis and effects on brain function (such as talking, learning, and memory).
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 is greater in younger women of normal or low weight. Care should be taken to exercise safely, because exercise carries the risk of injury to bones and muscles.
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 may be lowered in these women. However, it is very important to have a cancer risk assessment and counseling 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 menopause or the symptoms of menopause.
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.
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 5-A-Day website.
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.
Changes to This Summary (06/14/2007)
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.
This summary was completely reformatted. An image and some content were also added.
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.
To Learn More
Call
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.
Web sites and Organizations
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. There are also many other places where people can get materials and information about cancer treatment and services. Local hospitals may have information on local and regional agencies that offer information about finances, getting to and from treatment, receiving care at home, and dealing with problems associated with cancer treatment.
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.
LiveHelp
The NCI's LiveHelp service, a program available on several of the Institute's Web sites, provides Internet users with the ability to chat online with an Information Specialist. The service is available from 9:00 a.m. to 11:00 p.m. Eastern time, Monday through Friday. Information Specialists can help Internet users find information on NCI Web sites and answer questions about cancer.
Write
For more information from the NCI, please write to this address:
- NCI Public Inquiries Office
- Suite 3036A
- 6116 Executive Boulevard, MSC8322
- Bethesda, MD 20892-8322
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.
People who are at high risk for a certain type of cancer may want to take part in a clinical trial. 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 prevention methods, the risks involved, and how well they do or do not work. If a clinical trial shows that a new method is better than one currently being used, the new method may become "standard."
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.
2007-06-14
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