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Falsely Negative Mammograms
Missed cancers are particularly common in pre-menopausal women owing to the dense and highly glandular structure of their breasts and increased proliferation late in their menstrual cycle (10, 11). Missed cancers are also common in postmenopausal women on estrogen replacement therapy, as about 20 percent develop breast densities that make their mammograms as difficult to read as those of pre-menopausal women (12).
About one-third of all cancers— and more still of pre-menopausal cancers, which are aggressive, even to the extent of doubling in size in one month, and more likely to metastasize— are diagnosed in the interval between successive annual mammograms (2, 13). Pre-menopausal women, particularly, can thus be lulled into a false sense of security by a supposedly negative result on an annual mammogram and fail to seek medical advice.
Falsely Positive Mammograms
Mistakenly diagnosed cancers are particularly common in pre-menopausal women, and also in postmenopausal women on estrogen replacement therapy, resulting in needless anxiety, more mammograms, and unnecessary biopsies (14, 15). For women with multiple high-risk factors, including a strong family history, prolonged use of the contraceptive pill, early menarche, and nulliparity— just those groups that are most strongly urged to have annual mammograms— the cumulative risk of false positives increases to "as high as 100 percent" over a decade's screening (16).
Overdiagnosis and subsequent overtreatment are among the major risks of mammography. The widespread and virtually unchallenged acceptance of screening has resulted in a dramatic increase in the diagnosis of ductal carcinoma-in-situ (DCIS), a pre-invasive cancer, with a current estimated incidence of about 40,000 annually. DCIS is usually recognized as micro-calcifications and generally treated by lumpectomy plus radiation or even mastectomy and chemotherapy (17). However, some 80 percent of all DCIS never become invasive even if left untreated (18). Furthermore, the breast cancer mortality from DCIS is the same— about 1 percent— both for women diagnosed and treated early and for those diagnosed later following the development of invasive cancer (17). That early detection of DCIS does not reduce mortality is further confirmed by the 13-year follow-up results of the Canadian National Breast Cancer Screening Study (19). Nevertheless, as recently stressed, "the public is much less informed about overdiagnosis than false positive results. In a recent nationwide survey of women, 99 percent of respondents were aware of the possibility of false positive results from mammography, but only 6 percent were aware of either DCIS by name or the fact that mammography could detect a form of 'cancer' that often doesn't progress" (20).
In 1992 Congress passed the National Mammography Standards Quality Assurance Act requiring the Food and Drug Administration (FDA) to ensure that screening centers review their results and performance: collect data on biopsy outcomes and match them with the original radiologist's interpretation of the films (21). However, the centers do not release these data because the Act does not require them to do so. It is essential that this information now be made fully public so that concerns about the reliability of mammography can be further evaluated. Activist breast cancer groups would most likely strongly support, if not help to initiate, such overdue action by the FDA.
from the “Los Angeles Times”: Mammography Radiates Doubt
European Research Study confirms Mammography’s Ineffectiveness
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16. Christiansen, C. L., et al. Predicting the cumulative risk of false-positive mammograms. J. Natl. Cancer Inst. 92( 20): 1657– 1666, 2000.
17. Napoli, M. Overdiagnosis and overtreatment: The hidden pitfalls of cancer screening. Am. J. Nurs., 2001, in press.
18. Baum, M. Epidemiology versus scaremongering: The case for humane interpretation of statistics and breast cancer. Breast J. 6( 5): 331– 334, 2000.
19. Miller, A. B., et al. Canadian National Breast Screening Study-2: 13-year results of a randomized trial in women aged 50– 59 years. J. Natl. Cancer Inst. 92( 18): 1490– 1499, 2000.
20. Black, W. C. Overdiagnosis: An under-recognized cause of confusion and harm in cancer screening. J. Natl. Cancer Inst. 92( 16): 1280– 1282, 2000.
21. Napoli, M. What do women want to know. J. Natl. Cancer Inst. Monogr. 22: 11– 13, 1997.
Excerpted from “Dangers and Unreliability of Mammography: Breast Examination is a Safe, Effective and Practical Alternative”, by Samuel S. Epstein, Rosalie Bertell, and Barbara Seaman, International Journal of Health Services, Volume 31, Number 3, 2001
Samuel S. Epstein, M.D.
Chairman, Cancer Prevention Coalition
c/o University of Illinois at Chicago
School of Public Health, M/C 922
2121 W. Taylor Street
Chicago, IL 60612