Women Are Tolerant About False-Positive Mammography
ABSTRACT & COMMENTARY
Synopsis: Mammography is a widely accepted screening tool for the detection of early breast cancer. Recently, it has been recognized that the likelihood of a false-positive mammogram for those who undergo annual examinations is substantial. In this nationwide survey of women, an understanding and tolerance for this untoward occurrence was demonstrated.
Source: Schwartz LM, et al. BMJ 2000;320:1635-1640.
Mammography has effectively been promoted as a preventive measure to reduce the risk of dying from breast cancer. In the United States, for example, the great majority of women older than the age of 40 have had at least one mammogram.1 Yet it has been estimated that almost 50% of women who have annual mammograms for 10 years will have at least one false- positive reading, and this might result in additional and more intensive testing and psychological stress.2 The purpose of this study was to determine women’s understanding and attitudes about false-positive mammography and their understanding of ductal carcinoma in situ (DCIS). The latter was selected because early detection of DCIS may actually result in unnecessary treatment in at least some patients.3
Participants in this study were 479 women aged 18-97 who did not have a history of breast cancer. Painstaking efforts were made to sample the population in a manner that would reflect the general population of American women. Thus, the sample was derived from all 50 states and included individuals of all socio economic classes, ages, and ethnicity. However, only individuals with phones were included (by necessity) and, although repeated efforts were made to improve the questionnaire return rate, only about 65% of those invited were included in the final analysis. Thus, the sample turned out to be slightly wealthier, more educated, and less racially diverse than originally intended. Most of the women reported having had at least one mammogram: 35% of those younger than 40 years, 87% of those in their 40s, 93% of women aged 50-69, and 87% of women aged 70 or older. In fact, 76 women (16%) had experienced a false-positive mammogram.
The results indicate that women were well aware of the risk of false positives. Their median estimate of the false-positive rate for 10 years was 20%. Furthermore, it appeared that they were tolerant of false positives: 63% thought that 500 or more false positives per life saved was reasonable and 37% would tolerate 10,000 or more. Even the women who had experienced false-positive mammography, when analyzed separately, had the same level of tolerance for false positives as the general sample. Furthermore, well over half (62%) would not consider the risk of false-positive results when deciding whether to have mammography. Only 8% thought that mammography could harm a woman without breast cancer, and 94% discounted the possibility of non progressive breast cancers (e.g., DCIS) as a reason to do without mammography.
Thus, almost all (99%) of the 479 women knew about the risk of false-positive mammograms, and they did not seem to think that false-positive mammograms should influence their decisions about screening. This tolerance was not explained by overly optimistic expectations about the sensitivity or use of mammograms because, when questioned, they demonstrated a remarkable understanding of the limitations of the procedure. Nonetheless, only 6% were aware of the possibility of DCIS. However, when given a brief explanation of this diagnosis and the implications that some might be diagnosed and treated for a condition that might not have progressed, many, especially in the younger age groups, responded that they would consider this fact in their future screening practice.
Schwartz and colleagues conclude that women are less concerned about the possibility of false-positive testing than expected, but are less aware that screening could detect cancers that may never progress. They suggest that educational programs may aim at a better understanding of this screening outcome.
COMMENT by William B. ErshleR, MD
A conclusion that can be drawn from this report is that efforts at public education regarding mammography have been, for the most part, successful. Women included in this survey were well informed and had no preconceived or untenable bias either in favor or against mammography. Although, when asked, their estimates of the false-positive rates were somewhat less than what experts predict (20% vs 47%), they held no exaggerated notion of perceived harm (only 8% believed that there could be harm from repeated mammography) or exaggerated benefit. For example, most women believed that repeated mammography was better than a single study, but they placed the value of annual mammography well below other preventive measures such as smoking cessation, exercise, and low-fat diets. It seems the general population of women are tuned in to the pluses and minuses of mammography better than some might have predicted. In fact, it would be curious to see how women in the profession (e.g., doctors and nurses) fared on the same questionnaire. We might be surprised and a little embarrassed.
The population sampled wasn’t truly reflective of the general population, but it came close. Although those sampled were better educated and wealthier, the biggest variance was the under-representation of minorities. Again, it would be difficult to predict whether minority women have the same understanding of the limitations and tolerance for errors (false positives) as the population studied. Before reading the current report, I might have been tempted to hazard a guess—but I know better now. The current research has clearly shown that in matters of psychological and social response, we medical oncologists can sometimes be way off base. To better predict how minority women would feel about false-positive mammography, further scientific inquiry will be required.
References
1. Norrish AE, et al. Int J Cancer 1998;77:511-515.
2. Lerman C, et al. Health Psychol 1991;10:259-267.
3. Ernster VL, Barclay J. J Natl Cancer Inst Monogr 1997;151-156.
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