The NCAB said that women who are at higher than average risk should seek expert medical advice about beginning mammography before age 40 and about their screening frequency when they are in their 40s.
The Board defined higher risk women as those who have had breast cancer; women carrying identified genetic alterations that may make them more susceptible to breast cancer; women in families in which multiple family members are affected with breast cancer, generally at younger ages; those with breast disease that may predispose them to cancer or those having had two or more breast biopsies for benign disease; women with 75 percent or more dense breast tissue on previous mammograms that made mammography reading difficult; or women having a first birth at age 30 or older. Women without these risk factors are considered to be at average risk of developing breast cancer.
Because of the limitations of mammography, the Board stated that a clinical breast examination by a health care provider is an important part of regular, routine health care for women.
The Board stated that health insurers, including managed care organizations, should pay for mammography for higher risk women at any age and for all women beginning at 40. "The Board concluded that there is enough evidence to support a woman's decision to begin screening in her 40s," said Barbara Rimer, Dr. P.H., board chair, professor and director of cancer prevention, detection, and control research at Duke University, Durham, N.C.
"But the Board also wanted women and their providers to be informed fully about both the benefits and limitations of mammography so they can make informed decisions," Rimer added.
The NCI decided in 1993 not to recommend universal mammography screening beginning at age 40 because at that time there was not clear scientific evidence that women in their 40s undergoing regular screening have a reduced risk of dying of breast cancer. For many years, the evidence for women age 50 and older has shown clear benefit.
In reaching its conclusions, the National Cancer Advisory Board, a presidentially appointed committee that advises and consults with the director of the NCI, considered updated findings from breast cancer screening studies presented in January at an National Institutes of Health Consensus Development Conference. These new data show that regular screening mammography of average risk women in their 40s reduces deaths from breast cancer by about 17 percent.
In addition to the benefits of screening, the Board outlined the limitations of mammography. In particular, it referred to the high percentage (compared to women over age 50) of abnormal mammograms that are not cancer, but require further testing -- another mammogram, fine needle aspiration, ultrasound, or biopsy. Estimates are that a women who has a yearly mammogram in her 40s has about a 30 percent chance of having a "false-positive" mammogram.
Another limitation of mammography for women in their 40s is the difficulty of detecting tumors in the denser breasts of younger women. About 25 percent of breast tumors are missed in women in their 40s compared with 10 percent of tumors for women in their 50s.
Research is under way in imaging technology such as magnetic resonance imaging, breast ultrasound, and breast-specific positron emission tomography to overcome these limitations.
In addition to imaging technologies, NCI-supported scientists are exploring methods to detect traces of breast cancer in blood, urine, or nipple aspirates, and to detect genetic alterations in women who are at increased risk for breast cancer.
NCAB also recommended that the NCI take the following actions:
The Board statement, a link to Answers and Questions About Mammography Screening, and a list of the Board members are listed below.
The risk of developing breast cancer is not the same for all women. Several expert groups and professional organizations have examined the available data on mammography screening in women ages 40 to 49, and have reached different conclusions. Current mammography recommendations for women 40 to 49 are, of necessity, interim in nature and subject to change as new data continue to be collected. This statement reflects the perspective of the National Cancer Advisory Board.
Recommendations
To assist women ages 40 to 49 who seek definitive advice on mammography, the National Cancer Institute (NCI) should recommend regular screening mammograms between ages 40 and 49 years for women at average risk. (All women who do not fulfill criteria for higher risk, as defined on the next page, are assumed to be at average risk.) For women 40 to 49 years of age, it is prudent to have mammograms every one to two years.
Some women are at higher risk (see below) than others. Women of higher risk should seek expert medical advice about beginning mammography before age 40 and to determine their mammography schedule in the 40s. Mammography for women at higher risk is described in more detail below.
The NCI should continue to recommend regular (every one to two years) mammograms for women in their 50s and older, as advised by all professional organizations.
Benefits
The benefit of mammography is detection of cancer early when it is more easily treated with a better outcome. Regular screening mammography in average risk women ages 40 to 49 reduces deaths from breast cancer by about 17 percent. By early detection of breast cancer, treatment is not only more effective but potentially less disfiguring and toxic. Women whose breast cancers are found by mammography may also be able to have surgery that spares part of the breast.
Limitations of Mammography
No medical test is always 100 percent accurate, and mammography is no exception. Research is underway to improve the technology which will lead to better accuracy in screening with mammography.
While women 40 to 49 and older may benefit from having regular mammograms, some cancers will be missed by this test (as many as 25 percent of breast cancers for women ages 40 to 49). That is why it is important that a clinical breast examination by a health care provider should be included as part of regular, routine health care.
Distinguishing early cancers from suspicious, but not cancerous, breast abnormalities found on a mammogram is more difficult in younger women. These "false positive" mammograms require careful attention, including breast biopsies, to assure a woman that she does not have breast cancer. It is estimated that if a woman got mammograms every year between 40 to 49, she would have about a 30 percent chance of having a "false positive" mammogram result. Current research is directed towards improving the accuracy of mammograms to reduce the still high proportion of "false positives" among women 40 to 49 and, for that matter, other ages.
Who Pays for Mammograms?
For women within the age and risk groups recommended to have mammograms, all third party payers (e.g., health insurers and managed care organizations) should pay for mammography.
Mammograms for Women at Higher Risk of Breast Cancer
Women who have a higher risk of breast cancer, or who suspect that they may be prone to breast cancer, should seek good medical advice about when and how often to have mammograms, and should also practice other approaches, including examinations by health professionals, to detect this disease early when treatment is most effective. Elevated risk of breast cancer is associated with the following conditions: (1) having had a previous breast cancer; (2) laboratory evidence that the woman is carrying a specific mutation or genetic change that increases susceptibility to breast cancer; (3) 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; (4) having had a diagnosis of other types of breast disease (not cancer but a condition that may predispose to cancer) on a breast exam or having had two or more breast biopsies for benign disease, even if no atypical cells are found; and (5) having so much dense breast tissue (above 75 percent) on a previous mammographic examination that clear reading is difficult; and (6) having a first birth at age 30 or older. Women will need to consult a health professional to determine if some of these conditions are present.
Background
The controversy over mammography for women 40 to 49 is not new. In 1993, the NCI made the difficult decision to withdraw its prior recommendation for routine screening for women at these ages. Since then, new studies have found additional scientific evidence of a reduction in breast cancer mortality from screening mammography. Currently available data are from seven randomized studies in which women were assigned to either routine mammography or usual care, and thereafter, followed for cancer occurrences and mortality from breast cancer.
By combining available data from the seven randomized studies around the world, about a 17 percent reduction in breast cancer mortality was found for those who were invited for screening. To many, but not all experts this is statistically significant. This level of mortality reduction appears impressive, but is actually difficult to detect with a high level of certainty because the seven mammography studies differ with regard to study design and implementation, age composition of participants and other factors. The currently observed beneficial effect of mammography might increase, decrease or disappear over time. There may be unexpected late beneficial or harmful effects of screening mammography that cannot be detected presently.
In 1996, in the United States, 184,000 women were diagnosed with breast cancer; about 31,000 of these women were aged 40 to 49. The chance of being diagnosed with breast cancer over the decade of 40 to 49 is one in 66 women, or about 2 percent. In 1996, 44,000 women died from breast cancer; of those, 4,700 women were aged 40 to 49. A woman 40 to 49 has a 0.3 percent chance of dying from breast cancer before age 50.
Future Research
To improve the quality, analyses, interpretation and dissemination of data from the seven randomized studies of screening mammography (and other future studies), the NCAB recommends that the following actions be undertaken as soon as possible:
Questions and Answers About Mammography Screening
CHAIRPERSON
Barbara K. Rimer, Dr. P.H. Director-Cancer Prevention, Detection and Control Research Program Professor-Community and Family Medicine Duke University Comprehensive Cancer Center Durham, NC 27710
MEMBERS
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