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Editorials |
1 From the International Society of Radiology (O.W.L.) and National Council on Radiation Protection and Measurements (D.A.S.), 7910 Woodmont Ave, Suite 400, Bethesda, MD 20814. Received August 17, 2005; final version accepted September 2. Address correspondence to O.W.L.
Even though mammography has had a strong positive effect on the earlier and more accurate diagnosis of breast cancer, the acceptance of mammography for individuals suspected of having breast cancer, for population screening, and for follow-up studies has occurred amid continuing controversies.
The National Council on Radiation Protection and Measurements (NCRP) rejoined the debate with a definitive 390-page report on mammography that summarizes the arguments of the past 2 decades and reviews the results of the many studies on the value of mammography, particularly for screening. In this report, the NCRP concludes that the evidence supports the value of screening in asymptomatic women 40 years of age and older (1). The new report number 149 expands greatly on the NCRP's first report on mammography in 1986 (2).
When Robert L. Egan developed a reproducible mammographic technique in 1960, his first challenge was to convince other radiologists that they could produce clinically valid images and interpret them (3). In the same early months, Egan and a growing number of radiologist followers had to persuade surgeons and gynecologists that patients who were suspected of having breast cancer should undergo mammography before planned mastectomies. Pathologists had to be convinced that a valid correlation between radiologic and pathologic findings was inherent in the new imaging technique. Over time, those battles were won.
The next challenge came when advocates began to create screening programs in which asymptomatic women underwent periodic mammography. The storied Health Insurance Plan screening study (4) in New York City and the subsequent Breast Cancer Detection Demonstration Project, which was cosponsored by the American Cancer Society and the National Cancer Institute, provided evidence that periodic mammography allowed detection of early malignant and even premalignant changes that were not recognized by women or their physicians during physical examination. Noting the long-established 50%, 5-year breast cancer survival statistic in the United States, mammography proponents hailed screening programs as allowing early detection, the depiction of smaller lesions, more definitive surgery, and a brighter tomorrow. Critics countered that early detection was a factor of lead-time bias. There could be no more cancers detected than existed—unless mammographers were making false-positive diagnoses or repeated exposure to radiation provoked cancerous changes in normal breast tissue. Charges on both sides of the argument were made during a 1977 National Institutes of Health consensus conference and were echoed by the national press (5). The National Institutes of Health declined to distinguish between clinical mammography and screening mammography, and the acceptance of both ebbed strongly.
Mammographic techniques changed for the better. Some radiologists liked the edge enhancement advantages of xeromammography. Film manufacturers developed a one-screen mammographic film that cut exposures by 90%. Equipment manufacturers offered dedicated low–kilovolt peak equipment. Compression techniques became accepted.
Still, the criticisms continued. The American Cancer Society, National Cancer Institute, American College of Radiology, and others issued policy statements supporting mammography for screening and clinical use. By now, many of the critics relied on statistics. Was there any reduction in mortality from breast cancer? Could a change be credited to mammography or was increased salvage based on improved surgical techniques, postsurgical follow-up with radiation, and chemotherapy? Neither side convinced the other, but for whatever combination of causes, the 5-year survival rate began to show a positive change (6,7).
In 1986, at the urging of the American Cancer Society, the American College of Radiology developed a voluntary credential program for mammography facilities. The American Cancer Society encouraged women to bypass their physicians and undergo screening mammography at radiology facilities that met the American College of Radiology standards. Screening mammography became a Medicare benefit and was the first screening program to be covered by the federal program. In 1992, the U.S. Congress enacted the Mammography Quality Standards Act (42 USC 263b), which, in effect, made the American College of Radiology standards mandatory for any facility that performed mammography. Elaborate programs of state inspections were created by the U.S. Food and Drug Administration's Center for Devices and Radiological Health, which implemented the federal mandate (8).
A 1997 National Institutes of Health consensus conference panel stated that it could not make a firm recommendation about whether women should undergo screening mammography (9). This was renounced by Richard Klausner, the director of the National Cancer Institute, and was rejected by the U.S. Senate by a 98 to 0 vote (10). By now, any controlled sample study was impossible in the United States because—despite all of the furor and controversy—it would be unacceptable to deny mammography to any group of women. New studies came from Canada and Sweden with results that were just as controversial as those from earlier studies in the United States.
In 1990, the NCRP and the American Cancer Society recognized that drastic changes in mammographic concepts and techniques would justify a revised report. An NCRP scientific committee began work amid vigorous controversies about techniques and public policy. The NCRP committee's effort came to fruition in August 2005 with the publication of report number 149 (1), which was a compendium of information about mammographic practice, current techniques, equipment, alternate imaging modalities, radiation protection programs, quality assurance programs and audits, and benefit and risk analyses.
The result was that "mammography, in conjunction with physical examination, is the method of choice for early detection of breast cancer. Other methods should not be substituted for mammography in diagnosis or screening, but may be useful adjuncts in specific diagnostic situations" (1).
In effect, the NCRP reaffirmed that 40 years of experience with mammography for clinical detection, surveillance, and population screening was valid and should be continued.
Why did it take 15 years to produce this comprehensive report? The NCRP, as a federally chartered scientific advisory body, works on the basis of consensus. Volunteer committee members are selected for their expertise and contributions to the topic. It may take the committee several years to agree on a draft. That draft then is circulated to the 100 council members for review and balloting. The draft is also sent to honorary council members, collaborating and special liaison organizations, and professional societies for their review and comment. That feedback is then compiled by the NCRP secretariat and forwarded to the committee for response, acceptance, rejection, modification, and resubmission. The product of all this effort is a mainstream statement about mammography and about the continuing controversies. In this instance, the years of effort allowed the final report to reflect the resolution of some major arguments about mammography issues.
Where the 1997 National Institutes of Health consensus group waffled on the value of population screening of women beginning at age 40, the NCRP report asserted that such programs have "a positive benefit-cost ratio" (1).
The report asserts that with multiple screens the excess number of breast cancer cases is substantially more than for a single screen with a maximum percentage increase in subsequent lifetime breast cancer cases of 0.1% for women first screened at age 40. However, even a 1% reduction in breast cancer mortality rates more than offsets the increased risks of breast cancer mortality and the benefit is substantial for higher reductions in the mortality rate. The pattern of maximal benefit with respect to the age at which screening starts is somewhat different than that for a single screen in terms of reduced breast cancer deaths, since under the present model benefits will extend to age 84 for all women, and hence the benefit for younger women compared with older women is relatively greater under the multiple as opposed to single-screen scenario. This is emphasized even more when the benefit is presented in terms of women-years of life saved.
In reaching its conclusions regarding the effect of radiation exposure during mammography, the NCRP committee used the linear-nonthreshold dose-response model, which provides a conservative approach (11).
The amount of radiation received by a woman in the course of annual screening mammography performed by using current techniques is too low to observe direct effects. Thus, continuing arguments about the value and risks of screening depend on statistical analyses and meta-analyses of national studies, with the same studies being cited to attack or support screening programs. The NCRP report number 149 will not be the final word in the debate, but it does offer a comprehensive look at the practice of mammography in the 21st century and offers a solid endorsement of the favorable benefit-cost ratios in properly conducted screening programs.
The report is available from the NCRP publications Web site, http://NCRPpublications.org, in both softcopy and hardcopy formats.
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