National Cancer Institute
Posted Date: Feb 20, 2007
Doctors cannot always explain why one person gets cancer and another does not. However, scientists have studied general patterns of cancer in the population to learn what things around us and what things we do in our lives may increase our chance of developing cancer.
Anything that increases a person's chance of developing a disease is called a risk factor; anything that decreases a person's chance of developing a disease is called a protective factor. Some of the risk factors for cancer can be avoided, but many cannot. For example, although you can choose to quit smoking, you cannot choose which genes you have inherited from your parents. Both smoking and inheriting specific genes could be considered risk factors for certain kinds of cancer, but only smoking can be avoided. Prevention means avoiding the risk factors and increasing the protective factors that can be controlled, so that the chance of developing cancer decreases.
Although many risk factors can be avoided, it is important to keep in mind that avoiding risk factors does not guarantee that you will not get cancer. Also, most people with a particular risk factor for cancer do not actually get the disease. Some people are more sensitive than others are to factors that can cause cancer. Talk to your doctor about methods of preventing cancer that might be effective for you.
The purposes of this summary on breast cancer prevention are to:
- Give information on breast cancer and how often it occurs.
- Describe breast cancer prevention methods.
- Give current facts about which people or groups of people would most likely be helped by following breast cancer prevention methods.
You can talk to your doctor or health care professional about cancer prevention methods and whether they would be likely to help you.
The breast consists of lobes, lobules, and bulbs that are connected by ducts. The breast also contains blood and lymph vessels. These lymph vessels lead to structures that are called lymph nodes. Clusters of lymph nodes are found under the arm, above the collarbone, in the chest, and in other parts of the body. Together, the lymph vessels and lymph nodes make up the lymphatic system, which circulates a fluid called lymph throughout the body. Lymph contains cells that help fight infection and disease.
When breast cancer spreads outside the breast, cancer cells are most often found under the arm in the lymph nodes. In many cases, if the cancer has reached the lymph nodes, cancer cells may have also spread to other parts of the body via the lymphatic system or through the bloodstream.
See the following PDQ® summaries for more information on breast cancer:
- Screening for Breast Cancer
- Breast Cancer Treatment
- Male Breast Cancer Treatment
- Breast Cancer and Pregnancy Treatment
Breast cancer is second only to lung cancer as the leading cause of cancer death among women in the United States. Breast cancer occurs in men also, but the number of new cases is small. Early detection and effective treatment is expected to reduce the number of women who die from breast cancer, and development of new methods of prevention continue to be studied.
Breast cancer can sometimes be associated with known risk factors for the disease. Many risk factors can be changed but not all can be avoided. For example, women who inherit mutations (changes) in specific genes, such as BRCA1 or BRCA2, have a higher risk of developing breast cancer. High-risk genetic mutations are risk factors that cannot be changed. Researchers are looking for ways to prevent breast cancer in women with these genetic changes.
Estrogen, a , a hormone produced by the produced by the ovaries, appears to increase a woman's risk for , appears to increase a woman's risk for developing breast cancer. A woman's exposure to estrogen and her risk of breast cancer is increased in the following ways: developing breast cancer. A woman's exposure to estrogen and her risk of breast cancer is increased in the following ways:
- The use of estrogen-progestin therapy, also called combination hormone replacement therapy (HRT).
- Oral contraceptives ("the pill").
- Beginning to menstruate at age 11 or younger.
- Beginning menopause at a later age.
- Never being pregnant or having first child at an older age. Estrogen levels are lower during pregnancy and breast-feeding. A woman who has never had children, or who has her first child after the age of 35, has a higher risk of breast cancer than a woman who has her first child before the age of 20.
Exposure of the chest to radiation during during x-rays and and radiation treatment, especially at , especially at a young age, increases the risk of breast cancer beginning 10 years later. Although a small number of breast cancer cases can be linked a young age, increases the risk of breast cancer beginning 10 years later. Although a small number of breast cancer cases can be linked to radiation treatment, certain groups of people may be more at risk. Women who received radiation therapy for to radiation treatment, certain groups of people may be more at risk. Women who received radiation therapy for childhood childhood Hodgkin's lymphoma, for example, are at a greater risk for breast , for example, are at a greater risk for breast cancer later in life. Women at higher risk for breast cancer due to inherited changes in BRCA1 or BRCA2 genes have a further increased risk of breast cancer from exposure to cancer later in life. Women at higher risk for breast cancer due to inherited changes in BRCA1 or BRCA2 genes have a further increased risk of breast cancer from exposure to chest x-rays, especially before the age of 20. , especially before the age of 20.
Radiation therapy to treat cancer in one breast does not appear to increase the risk of developing cancer in the other breast.
Weight gain after menopause, especially after natural menopause and/or after age 60, is linked to increased breast cancer risk.
Drinking alcohol is linked to increased breast cancer risk. The more alcohol a woman drinks, the more the risk of breast cancer may increase, compared to a woman who drinks no alcohol.
- Selective Estrogen Receptor Modulators (SERMs)
SERMs are are drugs that act that act like estrogen on some like estrogen on some tissues in the body such as bones, but block the effect of estrogen on in the body such as bones, but block the effect of estrogen on other tissues. other tissues. Tamoxifen is a SERM that blocks the effect of estrogen on breast cancer is a SERM that blocks the effect of estrogen on breast cancer cells. A large study has shown that tamoxifen lowers the risk of getting cells. A large study has shown that tamoxifen lowers the risk of getting breast cancer in women who have an increased risk of getting breast cancer. breast cancer in women who have an increased risk of getting breast cancer. However, tamoxifen may also increase the risk of However, tamoxifen may also increase the risk of endometrial cancer, , stroke, and , and blood clots in in veins and in the veins and in the lungs. Women who are concerned that they may be at an . Women who are concerned that they may be at an increased risk of developing breast cancer should talk with their doctor increased risk of developing breast cancer should talk with their doctor about whether to take tamoxifen to prevent breast cancer. It is important about whether to take tamoxifen to prevent breast cancer. It is important to consider both the benefits and risks of taking tamoxifen.to consider both the benefits and risks of taking tamoxifen.
Raloxifene is another SERM that is being studied for the prevention of breast cancer. A study of is another SERM that is being studied for the prevention of breast cancer. A study of postmenopausal women with women with osteoporosis has shown that raloxifene lowered the risk of breast cancer for women at both high risk and low risk of developing the disease. It is not known if women who do not have osteoporosis would benefit in the same way. Like tamoxifen, raloxifene may increase the risk of blood clots in veins and in the lungs, but does not appear to increase the risk of endometrial cancer. has shown that raloxifene lowered the risk of breast cancer for women at both high risk and low risk of developing the disease. It is not known if women who do not have osteoporosis would benefit in the same way. Like tamoxifen, raloxifene may increase the risk of blood clots in veins and in the lungs, but does not appear to increase the risk of endometrial cancer.
- 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 made outside the ovaries from androgen, another hormone. , another hormone. Aromatase inhibitors stop an stop an enzyme called aromatase from turning androgen into estrogen. Possible harms from taking aromatase inhibitors include decreased called aromatase from turning androgen into estrogen. Possible harms from taking aromatase inhibitors include decreased bone density and effects on brain function (such as talking, learning, and memory). and effects on brain function (such as talking, learning, and memory).
- Prophylactic Mastectomy
The removal of both breasts may reduce the risk of breast cancer in women with a family history of breast cancer. Before making the decision to have of breast cancer. Before making the decision to have prophylactic mastectomy, it is important to undergo cancer risk , it is important to undergo cancer risk assessment and and counseling, and to carefully consider all the treatment options. In some women, prophylactic mastectomy may cause , and to carefully consider all the treatment options. In some women, prophylactic mastectomy may cause anxiety, , depression, and concerns about body image., and concerns about body image.
- Prophylactic Oophorectomy
The removal of one or both ovaries decreases the amount of estrogen made by the body and decreases the woman's breast cancer risk. Also, drugs may be taken to decrease the amount of estrogen made by the ovaries. The sudden drop in estrogen may cause the following symptoms of menopause to occur: of menopause to occur:
Exercising 4 or more hours a week may decrease hormone levels and help lower breast cancer risk. The effect of exercise on breast cancer risk is stronger in younger women of normal or low weight. Care should be taken to exercise safely, as physical activity carries the risk of injury to bones and muscles.
Studies have not proven a link between abortion and breast cancer.
Studies have not proven that certain environmental exposures (such as chemicals, metals, dust, and pollution) increase the risk of breast cancer.
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. Studies have shown, however, that eating a diet rich in 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. Studies have shown, however, that eating a diet rich in beta-carotene may decrease the risk of breast cancer. A diet rich in beta-carotene, may decrease the risk of breast cancer. A diet rich in beta-carotene, folate, and , and vitamins A and and C may reverse the higher risk of breast cancer linked to alcohol use. may reverse the higher risk of breast cancer linked to alcohol use.
- Smoking and Secondhand Smoke
Studies have not clearly shown that either smoking or being exposed to secondhand smoke affect the risk of breast cancer. affect the risk of breast cancer.
Changes were made to this summary to match those made to the health professional version.
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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."
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