Questions and Answers About Mammography Screening

1. What is the current position of the National Cancer Institute (NCI) on mammography screening?
The National Cancer Institute recommends that all women aged 50 and over get screening mammograms every one to two years.

The National Cancer Institute recommends that women in their 40s who are at average risk for breast cancer get screening mammograms every one to two years.

Women who are at higher risk of breast cancer should seek expert medical advice about whether to begin mammography before age 40 and to determine their mammography schedule in their 40s.

2. What does cancer risk mean?

Cancer risk means the possibility of developing the disease. Individual, medical, environmental, and genetic factors are known to increase a woman's chances of developing breast cancer. However, many of the risk factors for breast cancer are not known.

Every woman has some degree of risk for developing breast cancer during her lifetime; however, the risk of developing breast cancer is not the same for all women. Even a woman at higher risk will not necessarily develop breast cancer. (The known risk factors for breast cancer are described in question 11.)

3. What is meant by higher risk and average risk for breast cancer?

Women at higher risk for breast cancer are those who have one or more of the following conditions. Women will need to consult a health professional to determine if some of these are present:

  • personal history of breast cancer;
  • laboratory evidence that the woman is carrying a specific genetic mutation, or change, that increases susceptibility to breast cancer; for example, mutations in BRCA1 and BRCA2;
  • having a mother, sister, or daughter with a history of breast cancer or having two or more close relatives, such as cousins, with a history of breast cancer;
  • a diagnosis of a breast disease that may predispose a woman to breast cancer, or having had two or more breast biopsies for benign breast disease;
  • having so much dense breast tissue (above 75%) that a clear reading of a previous mammogram was difficult;
  • having a first birth at age 30 or older.

    The risk of getting breast cancer increases as a woman gets older. Women without the risk factors listed above are considered at average risk of developing breast cancer.

  • 4. Is this current position a change from NCI's former position?

    Yes. The NCI decided in 1993 not to recommend universal mammography screening beginning at age 40. At that time, there was not clear scientific evidence that women in their 40s undergoing regular screening mammograms had a reduced risk of dying of breast cancer.
    5. What was the reason for the recent change in NCI's recommendation?
    The National Cancer Advisory Board (NCAB), a Presidentially appointed committee that advises and consults with the Director of NCI and the Secretary of the Department of Health and Human Services, considered the updated findings from breast cancer screening studies presented in January 1997 at a National Institutes of Health Consensus Development Conference. These new data showed that regular screening mammography of women in their 40s reduces deaths from breast cancer by about 17 percent. The Board considered these data, and examined both the benefits and limitations of mammography and women's needs for information. The Board recommended to the Director of NCI in March 1997 that women between the ages of 40 and 49 get screening mammograms every one to two years if they are at average risk for breast cancer. Women at higher risk should seek expert medical advice about beginning mammography before age 40. NCI adopted the Board's recommendations.
    6. What other recommendations were made by the NCAB in its March statement?
    The Board also recommended that NCI undertake three actions as soon as possible: 1) Develop innovative methods to educate women, their physicians, and other health professionals regarding the established benefits and limitations of mammography screening in women ages 50 and over, and the current recommendations and state of knowledge regarding screening at earlier ages.

    2) Create a database and encourage the investigators conducting randomized mammography screening studies that include women ages 40–49 to provide primary data for combined analyses.

    3) Convene an independent Mammography Data Monitoring Board of experts to review, on an ongoing basis, the data from randomized mammography trials, and report regularly to the NCAB and the public on the progress of the trials.

    7. What are the responsibilities of the NCAB?
    The NCAB advises, assists, and consults with the NCI Director with respect to NCI activities and policies. The NCAB includes both scientists in various areas of laboratory, clinical, and prevention research and consumers from the community- at-large. The NCAB is composed of 18 non-Federal members appointed by the President for 6 year terms and 12 nonvoting ex officio Federal members. The NCAB meets quarterly.

    8. How will information about NCI's position be spread so women and doctors understand their options? Which organizations can women go to for information? Will there be a toll-free number to call?

    NCI will develop educational materials about screening mammography for a variety of audiences including women, physicians and other health care providers, the mass media, policymakers, cancer-related organizations, and insurance providers. These materials will also help women and health professionals determine an individual's breast cancer risk. NCI will work with the American Cancer Society, other government agencies, advocacy organizations, cancer centers, and other groups to educate the public and health professionals about the benefits and limitations of screening mammography.

    To spread the message, NCI will use its established channels for information dissemination and access. These include the Cancer Information Service's telephone service (1–800–4–CANCER) and its outreach component; the NCI World Wide Web site (, including PDQ, NCI's cancer information database; and the Journal of the National Cancer Institute.

    9. If a woman in her 40s decides to have a mammogram, who pays?
    Payment depends on a woman's insurance coverage and where she lives. Medicare covers one screening mammogram every two years for its beneficiaries who are in their 40s and every year for women in their 40s with a personal or family history of breast cancer. Forty states already require third-party payers to cover all or part of the cost of screening mammography for women in their 40s. An additional four states have legislation pending. Background on Breast Cancer and Mammography Screening

    10. What are the chances that woman in the United States might get breast cancer?

    As a woman ages, her chances of getting breast cancer increase. For example, present rates project that each year, out of 100,000 women:

  • in their 30s, 43 will be diagnosed with breast cancer and 8 will die of the disease.
  • in their 40s, 163 will be diagnosed with breast cancer and 29 will die of the disease.
  • in their 50s, 263 will be diagnosed with breast cancer and 59 will die of the disease.
  • in their 60s, 374 will be diagnosed with breast cancer and 91 will die of the disease.
  • 11. What are the known risk factors for breast cancer?

    Personal History: Women who have had one breast cancer may develop a second breast cancer.

    Genetic Alterations: Women carrying identified genetic alterations, such as those in BRCA1 or BRCA2, may make them more susceptible to breast cancer.

    Family History: The risk of getting breast cancer increases for a woman whose mother, sister, or daughter has had the disease or having two or more close relatives, such as cousins, with a history of breast cancer. About 5 percent of women with breast cancer have a hereditary form of this disease.

    Breast Changes: Women with certain benign breast changes known as atypical hyperplasia, or those having had two or more breast biopsies for benign disease, are at increased risk.

    Dense Breasts: Women with 75 percent or more dense breast tissue on a previous mammogram that made mammography reading difficult are at greater risk and are encouraged to have regular clinical breast exams.

    Late Child Birth: Women having a first birth at age 30 or older are also at increased risk.

    In addition, the incidence of breast cancer increases as a woman gets older. About 80 percent of breast cancers occur in women over the age of 50; the incidence is especially high for women over age 60. Breast cancer is uncommon in women under age 35.

    12. What are the best methods of detecting tumors as early as possible?

    Early detection is a means to detect breast cancer before the onset of symptoms. High-quality mammography, with or without clinical breast exam, is the most effective technology presently available to detect breast tumors. However, like any test, mammography has some limitations.

    13. What are the benefits from mammography screening?

    Several studies have shown that regular mammography screening can decrease a woman's chance of dying from breast cancer. In addition, early detection may prevent the necessity of removing lymph nodes, and in some cases may prevent the need for removing the entire breast or for undergoing chemotherapy.

    14. How does getting a mammogram affect survival in different age groups?

    Evidence about whether regular mammography can decrease a woman's chance of dying from breast cancer has come from seven large-scale, randomized screening trials in which the proportion of women who died from breast cancer in the group assigned to screening is compared to those who were not offered screening.

    There is no convincing evidence that a woman under age 40 with average risk (defined as having none of the risk factors listed in question 11, excluding age) of breast cancer will benefit from regular mammograms. Two factors contribute to reducing the benefit in this age group—the low incidence of breast cancer and the difficulty of "seeing" tumors with mammography in the relatively dense breasts of women younger than 40.

    For women in their 40s, there is recent evidence that screening with mammography on a regular basis reduces breast cancer deaths by about 17 percent.

    For women between the ages of 50 and 69, there is strong evidence that screening with mammography on a regular basis reduces breast cancer mortality by about 30 percent.

    15. What are some of the limitations of mammography?

  • Detection does not always mean saving lives: Even though mammography can detect tumors as small as 1 centimeter (more than 1/3 inch) in diameter, detecting a small tumor does not guarantee that a woman's life will be saved. Mammography may not help a woman with a fast-growing tumor that has already spread to distant parts of the body before being detected. Likewise, about 50 percent of women (those with slow-growing tumors) would not have died from breast cancer even if they had waited until a lump was felt, because their tumors are more treatable.

  • False Negatives: The breasts of younger women contain many glands and ligaments which make tumors more difficult to spot in mammograms. As women age, breast tissues become more fatty and tumors are more easily "seen" by mammography. Also, tumors in young women tend to grow faster than tumors in older women. They, therefore, appear more likely to grow between the scheduled mammograms. In the large mammography studies, about 25 percent of breast tumors were missed in women in their 40s compared to 10 percent of tumors for women in their 50s.

  • False Positives: Between 5 and 10 percent of mammograms are abnormal. Of those that are followed up with additional testing (another mammogram, fine needle aspirate, ultrasound, or biopsy), most will not be cancer in younger women. It is estimated that a woman who got mammograms every year between ages 40 and 49 would have about a 30 percent chance of having a "false positive" mammogram result.

  • Increased Cases of DCIS: Over the past 30 years, mammography has detected a higher proportion of small tissue abnormalities called ductal carcinomas in situ (DCIS), abnormal cells confined to the milk ducts of the breast. (The number of DCIS cases increased from 742 to 4,676 from l983 to l993.) Some experts believe that many of these tumors are not life-threatening, while others think that some will eventually spread (metastasize). Because there are no data to support either view, these abnormalities are commonly removed surgically.

  • Limitation of Data from Trials: None of the large-scale screening trials included sufficient numbers of minority women or women at high risk for breast cancer to make strong statements about effectiveness in such groups. In addition, the data do not permit a more detailed analysis of different age groups within the 40s.
  • 16. What percentage of women in different age groups receive mammograms?

  • Of women ages 40–49, 59.9 percent received a mammogram in the past two years.
  • Of women ages 50–64, 65.1 percent received a mammogram in the past two years.
  • Of women 65 and over, 54.2 percent received a mammogram in the past two years. (1993 figures from National Center for Health Statistics.)
  • 17. What technologies other than mammography are under development for breast cancer screening?

    New imaging technologies under development for breast cancer screening include magnetic resonance imaging, breast ultrasound, and breast-specific positron emission tomography. In addition to imaging technologies, NCI-supported scientists are exploring methods to detect products of breast cancer in blood, urine, or nipple aspirates, and to detect genetic alterations in women who are at increased risk for breast cancer.

    18. What research is NCI supporting to find better ways to prevent and treat breast cancer?

    Researchers are looking for ways to prevent breast cancer in women at high risk, including a large study to see if the drug tamoxifen will reduce cancer risk in women age 60 or older and in women ages 35 to 59 who have a pattern of risk factors for breast cancer. This Breast Cancer Prevention Trial will serve as a model for future studies of cancer prevention. Studies of diet, nutrition, and environmental factors could also lead to preventive strategies.

    In the treatment arena, the challenge is to make treatment more targeted and effective, and less toxic. Scientists are studying high-dose chemotherapy with bone marrow or stem cell transplantation to determine how this therapy can be used most effectively. Biological therapies, such as the HER2/neu antibody, could be more effective and have milder side effects than other treatments.

    Many studies are also under way to identify the causes of breast cancer, including an analysis of the role that alterations in the BRCA1 and BRCA2 genes play in the development of cancer. In addition, it will be important to understand the role of normal BRCA1 and BRCA2 genes in normal breast cells and the way these genes act to protect cells from becoming malignant. Scientists also are studying how these genes interact with other genes and with hormonal, dietary, and environmental factors to influence which cancers will develop and when.

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