What is screening?
Screening is looking for cancer before a person has any symptoms. This can help find cancer at an early stage. When abnormal tissue or cancer is found early, it may be easier to treat. By the time symptoms appear, cancer may have begun to spread.
Scientists are trying to better understand which people are more likely to get certain types of cancer. They also study the things we do and the things around us to see if they cause cancer. This information helps doctors recommend who should be screened for cancer, which screening tests should be used, and how often the tests should be done.
It is important to remember that your doctor does not necessarily think you have cancer if he or she suggests a screening test. Screening tests are given when you have no cancer symptoms.
If a screening test result is abnormal, you may need to have more tests done to find out if you have cancer. These are called diagnostic tests.
See the following PDQ summary for more information about cancer screening:
General Information About Breast Cancer
Key Points for This Section
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.
Each breast also contains 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 substances in lymph and 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 leading cause of death from cancer in American women.
Breast cancer occurs more often in white women than in black women. However, black women are more likely than white women to die from the disease.
Breast cancer occurs in men also, but the number of cases is small.
Health history can affect the risk of breast cancer.
Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn't mean that you will not get cancer. Talk with your doctor if you think you may be at risk for breast cancer. Risk factors for breast cancer include:
- Having certain gene mutations (changes), such as in the BRCA1 or BRCA2 genes.
- Menstruating at an early age.
- Older age at first birth or never having given birth.
- A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), or benign (noncancer) breast disease.
- A family history (first degree relative, such as a mother, daughter or sister) with breast cancer.
- Treatment with radiation therapy to the breast/chest.
- Breast tissue that is dense on a mammogram.
- Taking hormones such as estrogen and progestin for symptoms of menopause.
- Taking oral contraceptives ("the pill").
- Not getting enough exercise.
- Drinking alcoholic beverages.
- Being white.
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.
Breast Cancer Screening
Key Points for This Section
- Tests are used to screen for different types of cancer.
- Three tests are used by health care providers to screen for breast cancer:
- Other screening tests are being studied in clinical trials.
Tests are used to screen for different types of cancer.
Some screening tests are used because they have been shown to be helpful both in finding cancers early and in decreasing the chance of dying from these cancers. Other tests are used because they have been shown to find cancer in some people; however, it has not been proven in clinical trials that use of these tests will decrease the risk of dying from cancer.
Scientists study screening tests to find those with the fewest risks and most benefits. Cancer screening trials also are meant to show whether early detection (finding cancer before it causes symptoms) decreases a person’s chance of dying from the disease. For some types of cancer, the chance of recovery is better if the disease is found and treated at an early stage.
Clinical trials that study cancer screening methods are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site.
Three tests are used by health care providers to screen for breast cancer:
Mammography is the most common screening test for breast cancer. A mammogram is an x-ray of the breast. This test may find tumors that are too small to feel. A mammogram may also find ductal carcinoma in situ (DCIS). In DCIS, there are abnormal cells in the lining of a breast duct, which may become invasive cancer in some women.
Mammograms are less likely to find breast tumors in women younger than 50 years than in older women. This may be because younger women have denser breast tissue that appears white on a mammogram. Because tumors also appear white on a mammogram, they can be harder to find when there is dense breast tissue.
The following may affect whether a mammogram is able to detect (find) breast cancer:
- The size of the tumor.
- How dense the breast tissue is.
- The skill of the radiologist.
Women aged 40 to 74 years who have screening mammograms have a lower chance of dying from breast cancer than women who do not have screening mammograms.
Clinical breast exam (CBE)
A clinical breast exam is an exam of the breast by a doctor or other health professional. The doctor will carefully feel the breasts and under the arms for lumps or anything else that seems unusual. It is not known if having clinical breast exams decreases the chance of dying from breast cancer.
Breast self-exams may be done by women or men to check their breasts for lumps or other changes. It is important to know how your breasts usually look and feel. If you feel any lumps or notice any other changes, talk to your doctor. Doing breast self-exams has not been shown to decrease the chance of dying from breast cancer.
MRI (magnetic resonance imaging) in women with a high risk of breast cancer
MRI is a procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI). MRI does not use any x-rays.
MRI is used as a screening test for women who have one or more of the following:
MRIs find breast cancer more often than mammograms do, but it is common for MRI results to appear abnormal even when there isn't any cancer.
Other screening tests are being studied in clinical trials.
Thermography is a procedure in which a special camera that senses heat is used to record the temperature of the skin that covers the breasts. A computer makes a map of the breast showing the changes in temperature. Tumors can cause temperature changes that may show up on the thermogram.
There have been no clinical trials of thermography to find out how well it detects breast cancer or if having the procedure decreases the risk of dying from breast cancer.
Breast tissue sampling is taking cells from breast tissue to check under a microscope. Abnormal cells in breast fluid have been linked to an increased risk of breast cancer in some studies. Scientists are studying whether breast tissue sampling can be used to find breast cancer at an early stage or predict the risk of developing breast cancer. Three ways of taking tissue samples are being studied:
- Fine-needle aspiration: A thin needle is inserted into the breast tissue around the areola (darkened area around the nipple) to take out a sample of cells and fluid.
- Nipple aspiration: The use of gentle suction to collect fluid through the nipple. This is done with a device similar to the breast pumps used by women who are breast-feeding.
- Ductal lavage: A hair-size catheter (tube) is inserted into the nipple and a small amount of salt water is released into the duct. The water picks up breast cells and is removed.
Screening clinical trials are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site.
Risks of Breast Cancer Screening
Key Points for This Section
- Screening tests have risks.
- The risks of breast cancer screening tests include the following:
- Finding breast cancer may not improve health or help a woman live longer.
- False-negative test results can occur.
- False-positive test results can occur.
- Anxiety from additional testing may result from false positive results.
- Mammograms expose the breast to radiation.
- There may be pain or discomfort during a mammogram.
- The risks and benefits of screening for breast cancer may be different in different age groups.
Screening tests have risks.
Decisions about screening tests can be difficult. Not all screening tests are helpful and most have risks. Before having any screening test, you may want to discuss the test with your doctor. It is important to know the risks of the test and whether it has been proven to reduce the risk of dying from cancer.
The risks of breast cancer screening tests include the following:
Finding breast cancer may not improve health or help a woman live longer.
Screening may not help you if you have fast-growing breast cancer or if it has already spread to other places in your body. Also, some breast cancers found on a screening mammogram may never cause symptoms or become life-threatening. Finding these cancers is called overdiagnosis. When such cancers are found, treatment would not help you live longer and may instead cause serious side effects. At this time, it is not possible to be sure which breast cancers found by screening will cause problems and which ones will not.
False-negative test results can occur.
Screening test results may appear to be normal even though breast cancer is present. A woman who receives a false-negative test result (one that shows there is no cancer when there really is) may delay seeking medical care even if she has symptoms.
One in 5 cancers may be missed by mammography. False-negative results occur more often in younger women than in older women because the breast tissue of younger women is more dense. The chance of a false-negative result is also affected by the following:
False-positive test results can occur.
Screening test results may appear to be abnormal even though no cancer is present. A false-positive test result (one that shows there is cancer when there really isn’t) is usually followed by more tests (such as biopsy), which also have risks.
Most abnormal test results turn out not to be cancer. False-positive results are more common in the following:
The skill of the radiologist also can affect the chance of a false-positive result.
Anxiety from additional testing may result from false positive results.
False-positive results from screening mammograms are usually followed by more testing that can lead to anxiety. In one study, women who had a false-positive screening mammogram followed by more testing reported feeling anxiety 3 months later, even though cancer was not diagnosed. However, several studies show that women who feel anxiety after false-positive test results are more likely to schedule regular breast screening exams in the future.
Mammograms expose the breast to radiation.
Being exposed to radiation is a risk factor for breast cancer. The risk of breast cancer from radiation exposure is higher in women who received radiation before age 30 and at high doses. For women older than 40 years, the benefits of an annual screening mammogram may be greater than the risks from radiation exposure.
There may be pain or discomfort during a mammogram.
During a mammogram, the breast is placed between 2 plates that are pressed together. Pressing the breast helps to get a better x-ray of the breast. Some women have pain or discomfort during a mammogram.
The risks and benefits of screening for breast cancer may be different in different age groups.
The benefits of breast cancer screening may vary among age groups:
- In women who are expected to live 5 years or fewer, finding and treating early stage breast cancer may reduce their quality of life without helping them live longer.
- As with other women, in women older than 65 years, the results of a screening test may lead to more diagnostic tests and anxiety while waiting for the test results. Also, the breast cancers found are usually not life-threatening.
- In women in their 80s and 90s, decisions about screening should depend on the patient's health and the possible effect on quality of life.
- It has not been shown that women with an average risk of developing breast cancer benefit from starting screening mammography before age 40.
Women who have had radiation treatment to the chest, especially at a young age, are advised to have routine breast cancer screening. Yearly MRI screening may begin 8 years after treatment or by age 25 years, whichever is later. The benefits and risks of mammograms and MRIs for these women have not been studied.
There is no information on the benefits or risks of breast cancer screening in men.
No matter how old you are, if you have risk factors for breast cancer you should ask for medical advice about when to begin having breast cancer screening tests and how often to have them.
Changes to This Summary (11/25/2014)
Editorial changes were made to this summary.
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