Mammography: The Frightening Risk of False-Positive Results
By Barbara A. Biedrzycki, RN, MSN, AOCN, CRNP
Summary-A recently published study shows that during a 10-year period, one-third of 2400 women screened for breast cancer had abnormal results that required additional evaluation. The risk of a false-positive result increases with more screening. By the time a woman has 10 screening tests, the researchers estimate about a 50% risk of having at least one false-positive mammogram and a 25% risk of a false-positive clinical breast exam.
· Of 88 women diagnosed with breast cancer during the study period, 26.1% noticed an abnormality themselves and sought evaluation.
· For every $100 spent for breast cancer screening, an additional $33 was spent evaluating false-positive results. The cost in anxiety and psychological trauma is immeasurable.
· Advanced practice nurses need to reinforce the value of monthly breast self-examination and regular screening tests and educate women about the potential for false-positive results when referring for mammography.
Breast self-examinations (bses), clinical breast examinations (CBEs), and mammography all have been involved in controversial issues as our knowledge and skills in breast cancer detection evolve. And now, Elmore and colleagues have provoked quite a stir with their conclusions. Elmore et al conducted a retrospective record review of 2400 women screened for cancer during a 10-year period from July 1, 1983, through June 30, 1993. In their research, published in the April 16, 1998, New England Journal of Medicine, they estimate the cumulative risk of having at least one false-positive result after 10 screenings is 49.1% for mammograms and 22.3% for CBEs.1 Their data indicate that for every $100 spent on screening, about $33 in additional money was spent to evaluate false-positive results.
Elmore and colleagues wanted to determine the frequency and cumulative risks of false-positive results of screening mammograms and CBE, and the cost of additional testing necessitated by positive results. At Harvard Pilgrim Health Care, a large health maintenance organization (HMO) in Boston, researchers examined 2400 randomly selected computerized clinical records of females between ages 40-69 at the onset of the study. The women had 9762 screening mammograms and 10,905 clinical breast exams, which meant a median of four mammograms and five CBEs each during the 10-year study. The mammograms were read by 93 radiologists at 28 radiology facilities. CBEs were performed by 381 health care providers including internists, RNs, nurse practitioners, physician assistants, OB-GYNs, and surgeons. Providers with unknown credentials performed 20. The study provided no data regarding BSEs.
On average, the women in this study underwent breast cancer screening every two years. During the study period, 88 women were diagnosed with breast cancer.
· Fifty-eight were first recognized by screening mammography (50 within 12 months after mammography, 8 after more than 12 months).
· Seven were first recognized as a result of CBEs (4 within 12 months, 3 after more than 12 months).
· The remaining 23 were diagnosed after the women themselves noted an abnormality and sought evaluation.
False-Positive Results Calculated
Overall, 6.5% (631/9762) of the mammograms and 3.7% (402/10,905) of the CBEs resulted in false-positive readings. The highest number of false-positive mammograms (7.8%) and CBEs (6.0%) occurred in the 40-49 age group.
Statistics from 1994, which are the latest available, list breast cancer as the No. 1 cancer killer of females in age range 15-54.2 False-positive rates were higher for younger women than for older ones, and a false-positive test result of either type of screening was found in 31.7% of the women.
The authors noted that a woman's risk of having a false-positive result increased with more screening. Using a mathematical calculation (Bayesian model), Elmore et al estimated the cumulative risk of false-positive tests. The researchers projected the cumulative risk of having at least one false-positive result after 10 screening exams to be 49.1% for mammograms and 22.3% for CBEs.
Study Conclusions
Elmore et al concluded there is need for improved techniques to decrease the number of false-positive results and still maintain high sensitivity of breast cancer screenings with their associated psychological and economic consequences. (See figure, p. 11.)
They suggest immediate on-site radiological work-up of presumed positive mammograms and CBEs as one way to reduce the associated anxiety and psychological sequelae. The authors write, "Women should be educated about their chances of having an abnormality noted on breast-cancer screening tests, and health care providers should be trained to deal with positive results when they occur."
In the discussion section of their study, the authors write, "The possibility that radiologists in the United States are interpreting too many mammograms as abnormal should be investigated."1
As you might imagine, not only that statement, but the entire study may cause women to distrust mammography as an effective screening tool.
Controversy Erupts
In a fact sheet for its members, the American College of Radiology in Reston, VA, states, "The 10-year estimate was merely a projection, not an actual figure. A false-negative screening mammogram would be far worse than a false-positive mammogram."3
Daniel B. Kopans, MD, FACR, associate professor of radiology, assistant director of ambulatory care radiology, and director of breast imaging at Massachusetts General Hospital and Harvard Medical School in Boston, and Stephen A. Feig, MD, professor of radiology and director of breast imaging at Thomas Jefferson Medical Center in Philadelphia, are consultant to and member of, respectively, the American College of Radiology's breast cancer task force. In an editorial to the Washington Post, they stated, "We strongly support providing women with information concerning the advantages and limitations of breast cancer screening. . . . Although the American College of Radiology certainly is concerned about false positives causing additional anxiety, the alternative - false negatives due to less careful reading - is clearly not preferable. The additional mammograms have the potential to save lives."4
Kopans points out that some flaws in the research methodology may have led to exaggerated rates of cumulative false-positive rates in Elmore et al's study.
He questions if the women who had more screening studies were actually at higher risk for breast cancer or had breast problems that might have prompted higher recall rates requiring additional exams, films, or ultrasonography. Also, Kopans notes that recall rates are about half when the radiologists have previous films available for comparisons. The research data could have been interpreted better if the distinction was made between false-positive rates for initial and then subsequent mammograms as well as between interpretation with and without previous films for comparison.5
In this study, most women were referred to sites outside the HMO for the mammograms, and all radiologists who read the mammograms were board certified. The mammography Quality Standards Act requires all facilities to be certified by the Food and Drug Administration (FDA). That means the facility must demonstrate its compliance with federal standards for equipment, personnel, and practices.6
Cutting through the Confusion
BSE as part of the breast cancer screening triad was not mentioned in this study, but it is a concern for advanced practice nurses.
Women need education about possible false-positive screening tests and how to peform monthly BSEs. (See education sheet, inserted in this issue.) It is significant that in 26.1% of the breast cancers diagnosed during this study period, an abnormality leading to evaluation was first noticed by the women themselves. However, there is controversy about mammography effectiveness and BSE. (For a development from a major cancer group regarding BSE, see story, p. 12.) The American Cancer Society in Atlanta recommends annual mammograms and CBE for women over age 40.7 The society and the National Cancer Institute (NCI) in Bethesda, MD, agree on the need for monthly BSE but differ on the recommended frequency of mammograms.
The NCI differentiates between an average risk, which exists because of female sex and aging, and a higher than average risk. A higher risk exists when there is a personal history of breast cancer, evidence of specific genetic changes, a close relative with breast cancer, especially if diagnosed at an early age, or history of two or more breast biopsies.6 The NCI recommends mammograms every 1-2 years after age 40 for women at average risk. Mammography for women with higher risk is left to the discretion of the health care provider.6
In the end, practitioners must decide what is appropriate and necessary for patients, based on a thorough medical and family history and careful physical examinations.
References
1. Elmore J, Barton M, Moceri V, et al. Ten-year risk of false-positive screening mammograms and clinical breast exams. New Engl J Med 1998;338:1089-1096.
2. Elmore J, Barton M, Moceri V, et al. Ten-year risk of false-positive screening mammograms and clinical breast exams. N Engl J Med 1998;338:1089-1096.
3. American College of Radiology. False-positive mammograms. Fact Sheet. Reston, VA; 1998.
4. Kopans D, Feig S. Screening breast cancer facts. The Washington Post, April 27, 1998: A16.
5. Kopans D. Correspondence dated May 11, 1998.
6. National Cancer Institute. Understanding Breast Changes: A Health Guide for All Women. No. 97-3536. Cancer Information Service, Bethesda, MD.
7. American Cancer Society news release. The National Institutes of Health announces results from its consensus conference on mammography for women age 40-49. Jan. 24, 1997.
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