Based on their survey of women's attitudes about screening mammography, Schwartz and colleagues conclude that women are knowledgeable of the chance of a false-positive result and accept this risk as a consequence of undergoing screening mammography. It is not clear, however, whether the authors accurately assessed women's true tolerance of false-positive mammography results because their survey did not describe the spectrum of physical and psychological sequelae of a false-positive result (for example, additional diagnostic evaluations and associated morbidity and anxiety).1,2,3 Thus, the proportion of women who are tolerant of false-positive mammography results may have been overestimated because the possible harms of screening mammography were not fully described. Even so, 38% of women surveyed indicated that they would want to factor information about the consequences of false-positive results into their decision about undergoing screening mammography. If nearly 2 of every 5 women desire such information, then they should be informed of the possible harms, as well as the benefits, of screening mammography.
The authors attempt to bolster their conclusion by reporting that women who had both a positive mammography result and subsequent benign findings on tissue biopsy expressed the same high tolerance for false-positive results as all of the women surveyed. However, women who have positive mammography results that subsequently lead to biopsy account for only 25% of women with false-positive results.4 Thus, these women's tolerance of false-positive results may not accurately reflect the views of all women who have false-positive results. Women who undergo breast biopsy for positive results are often so relieved when they find out that they do not have breast cancer that they might understandably—but somewhat ironically—have a high tolerance of false-positive results.
Estimates that should be provided to a woman for informed decision making before mammography
Individual risk of invasive breast cancer and DCIS
Age-specific chance of an abnormal result
Age-specific chance of a false-positive result
Chance that mammography may miss cancer
Expected absolute reduction in risk of breast cancer deaths among women in her age group who undergo screening mammography compared with women who do not
The authors found that a significant proportion (55%) of women overestimate the benefit of mammography, and that only 25% accurately reported that the chance of dying of breast cancer would be reduced by 30% for a 60-year-old woman undergoing screening mammography. Nonetheless, Schwartz and associates conclude that the high tolerance for false-positive results is not explained by overly optimistic beliefs of the benefits of mammography. One interpretation of the results is that women do overestimate the benefit of screening and that such misperceptions may explain why some women did not want to factor information about the consequences of false-positives into their decision about screening mammography.
The authors found that few women (6%) were knowledgeable about ductal carcinoma in situ (DCIS). When women were informed about DCIS, 3 of every 5 women wanted to take into account the chance of it being detected when deciding whether to undergo screening mammography. This is an important finding and suggests that information about DCIS should be included in educational materials and discussions about the possible benefits and harms of screening mammography. We were involved in designing and writing a Web site (http://mammography. ucsf.edu/inform/index.cfm) that gives an example of how DCIS may be explained to women. The site states that
DCIS lesions contain cells that appear to be cancer but not all such lesions behave as cancer, ie, they will not spread outside the ducts and invade surrounding tissue nor will they be life threatening. In other words, only some DCIS will eventually become invasive cancer. What percentage will become invasive cancer is not known. Almost all women who have DCIS detected are treated by surgery, either a mastectomy (removal of the breast) or by lumpectomy (excision of the lesion) with or without radiation.
Additional information that could be conveyed to women is the absolute benefit of detecting DCIS. For example, for every 10,000 women aged 70 years and older screened for 10 years, 65 cases of DCIS will be detected and surgically treated with mastectomy or lumpectomy and only 1 death from invasive breast cancer averted.5
To encompass a range of individual preferences, women should be provided with estimates—in absolute terms—of the possible benefits and harms of mammography to make an informed decision about screening (see box). Women who easily tolerate the additional tests that are recommended following an abnormal screening result and want to do everything possible to decrease the chance of death from breast cancer, even if certain harms are involved, will likely choose to undergo screening mammography. On the other hand, women who feel that the small incremental risk of breast cancer death associated with not being screened is outweighed by the fairly high likelihood of a false-positive result, the additional testing, and the anxiety may rationally choose not to have screening mammography.
Figure 1.
This Web site, at http://mammography.ucsf.edu/inform/index.cfm, gives clinical information about ductal carcinoma in situ (DCIS)
Funding: Supported in part by Breast Cancer SPORE grant P50 CA 58207 from the National Cancer Institute, Bethesda, MD, and cooperative agreement 1 U01 CA 63740 from the NCI Breast Cancer Surveillance Consortium.
Competing interests: None declared
Authors: Dr Kerlikowske is assistant professor in the departments of Medicine and Epidemiology and Biostatistics at University of California, San Francisco (UCSF), School of Medicine and director of the Women Veterans Comprehensive Health Center. Dr Ernster is professor and vice chair, Department of Epidemiology and Biostatistics, and associate director for Cancer Epidemiology, Prevention and Control of the Comprehensive Cancer Center at UCSF.
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