Lessons from the Mammography Screening Controversy: Can We Improve the Debate?

The debate about screening mammography for women in their 40s has been ongoing for more than 25 years. In 1971, the Health Insurance Plan study reported that breast cancer screening reduced mortality rates for women aged 50 to 64 years but not for women aged 40 to 49 years [1]. Today, the debate is very much alive after the completion of eight randomized, controlled trials; a large demonstration project; at least three casecontrol studies; and five meta-analyses and the publication of hundreds of opinion pieces and editorials. In January 1997, a National Institutes of Health Consensus Development Conference [2] concluded that the available data do not warrant a single recommendation for mammography for all women in their forties. Each woman should decide for herself whether to undergo mammography. Two months later, the American Cancer Society, referring to the same evidence, took a different stand with their recommendation that all women in their 40s undergo annual mammography [3]. Shortly after that, the National Cancer Advisory Board's recommendation for performing mammography every 1 to 2 years was quickly adopted by the National Cancer Institute [4]. The debate, heated at times, has perhaps never been more contentious than in the past few months. With emotional outbursts at public meetings and in the press, positions seem to have hardened, and the discourse that might find common ground is not occurring. This controversy provides an opportunity to gain important insights into a policy problem in which there is, at substantial economic cost, a large benefit for a small number of persons and a small amount of harm for a larger number. Although some may have tired of this controversy, we believe that it should be pursued for two reasons. First, contentiousness may be getting in the way of rational decision making, at both the individual and policy levels. Second, there may be a reasonable middle ground. The purpose of this commentary is to identify the sources of disagreement and contention so that discussion and decision making can move ahead constructively. Anatomy of a Decision: Two Steps Medical decision making, whether for individual persons or for policymakers, involves two major steps, as described by Eddy [5]. The first step involves facts and the analysis of evidence. For mammography screening, the facts include a description of the options (screening or no screening), the possible outcomes of those options (cases of cancer diagnosed, lives extended, the effort of screening and workups, the effect of false-positive results, and costs), and the chances that any of these outcomes may occur. Step 1 should be relatively straightforward because, as Eddy notes, assuming there is some evidence to evaluate, it should be possible to get reasonable, open-minded people to agree on the results of this step [5]. The second step is more problematic because it concerns not facts but rather each decision maker's informed personal judgments about the importance of the outcomes and risks of each option: that is, values and utilities. The concept of informed decisions is important because uninformed decisions are more likely to be bad decisions and to lead to disappointment. Sources of Disagreement: What the Debate Is about The disagreement in this controversy is less about facts than it is about judgments. Thus, most participants in the debate, but not all, agree that the mortality benefit over 10 to 12 years is about 16% to 18%, or about 1 or 2 lives extended per 1000 women 40 to 50 years of age who are screened annually for 10 years [6]. This agreement should not be surprising because screening mammography has been studied for more than 30 years. However, perceptions of this mortality reduction and of judgments about the balance between benefits and possible harms and effort differ substantially. Description and Perception of Risk Description of Risk A central challenge in the mammography debate concerns how to describe benefit (reduction of risk) and harm (additional risk) fairly and completely so that individual persons as well as policymakers are well informed and can go to the next step of factoring in their own subjective values and judgments. The dramatic effect of how facts are framed or presented to a decision maker has been well studied in the cognitive psychology literature [7-10]. To take advantage of this effect, persons on different sides of the mammography debate have presented risk in very different ways, much like businesses trying to market a product. Thus, it sounds more impressive to state that mammography reduces the relative risk for death from breast cancer by 16% to 18% than to state that the absolute risk for death is reduced by 1 to 2 lives per 1000 women screened annually for 10 years [11]; however, both of these descriptive statements are correct. A different approach to stating the benefit would be to describe the number needed to screen over 10 years to prevent one death from cancer (about 500 to 1000) or the number of side effects incurred to prevent one death from cancer [12]. Another approach would be to state that the average amount of life gained by mammography screening for women in their 40s is only 3 days (Berry D. Personal communication), a number that sounds small. In contrast, a statement that about 800 women in their 40s in the United States would have their lives extended each year by universal screening sounds large. The point is that the different descriptions of the same facts may sound different. How to select a fair method with which to describe the facts is still uncertain. We need both additional research and open discussion about the ground rules for and principles behind informing people. Risk Perception and Misperception Regardless of the method used to describe the facts about risk reduction, an entirely separate set of features may affect a person's perception of that risk. Thus, some features of everyday life tend to carry both the message that breast cancer is a very common problem and the message that screening is effective in extending lives. Indeed, many women, especially those younger than 50 years of age, greatly overestimate their own risk for breast cancer and similarly overestimate the risk reduction possible from screening mammography [13-15]. Why might such overestimates occur? The field of cognitive psychology suggests that the availability heuristic may make persons perceive risks as higher than they actually are [16]. Nearly everyone knows someone who has received a diagnosis of breast cancer. It is a diagnosis that, when it occurs, is widely discussed and makes a lasting impression on anyone who hears of it. The availability of this mental impression has been shown to lead to an exaggerated sense of risk. Similarly, much everyday experience may suggest that mammography screening is more effective than it actually is in reducing breast cancer mortality. Breast cancer has never been a universally fatal disease, and most women in whom breast cancer is diagnosed actually die of something else. This was true even before widespread screening [17]. However, as more and more women are given a diagnosis by screening, the natural perception of each survivor is that screening saved her life. Although clinical trials show that screening in women 40 to 50 years of age sometimes does extend lives (because breast cancer mortality is reduced by 16% to 18% in this group), most survivors actually have a type of breast cancer that could have been treated as effectively when found later as a lump or that might never have caused problems. The problem is that for each survivor, there is no way to know whether screening caused survival, and it is only natural to want to believe that an unpleasant medical intervention has helped. Thus, the number of women who perceive benefit from screening is substantially greater than the actual number who receive benefit, and the impression of benefit is exaggerated. Given our problems in fairly communicating risk and the intuitive belief of benefit among survivors of breast cancer, it is not hard to understand how these perceptions can add fuel to the fire of disagreement. Disagreement about Effects of Screening on Quality of Life Although reduction of breast cancer-related mortality rates is the primary outcome in clinical trials, quality of life outcomes may be important as benefits or harms in decisions about screening. There is disagreement about both the non-mortality-related benefits and the harms of screening. Non-Mortality-Related Benefits of Screening Potential non-mortality-related benefits of screening include less intensive therapy (for example, lumpectomy rather than mastectomy) because disease detected earlier may require less aggressive treatment. However, although lumpectomy rates are increasing, mastectomy rates are not declining proportionately [18]. Furthermore, the decision to treat with lumpectomy does not depend greatly on finding cancer at a prepalpable stage, and factors other than tumor size enter into the treatment decision. It is not clear that more screening per se will substantially decrease mastectomy rates, although these rates may decline for other reasons. Peace of mind, another potential benefit of screening that is reported by many women after a negative result on a mammogram, is also in dispute. Statistically, at least, the reassurance that a woman should derive from a negative result on a screening mammogram is the difference between the probability of cancer before the mammogram and the probability of cancer after a negative result on the mammogram. For a woman 45 years of age, this is a probability difference of about 0.0012 (1.6 in 1000 before mammography 0.4 in 1000 after a negative result on a mammogram), or an absolute change of a little more than 0.1%. The degree of reassurance that many women report from a negative result on a mammogram appears to be out of proportion to this calculation.