Why don't doctors discuss cancer screening harms?

A few years ago, I attended a conference that included an exercise where attendees were asked how many patients they thought it was acceptable to diagnose and treat needlessly ("overtreat") in order to prevent one death from cancer. We stood at various points along a wall that represented different thresholds: at one end, 100 persons overtreated for every 1 life saved; at the other, 1 person overtreated for every 1 life saved. Not surprisingly, attendees held a wide range of opinions (I stood somewhere in the middle), but the exercise illustrated the tradeoff inherent in effective screening tests for breast, colorectal, and cervical cancer: for every person who benefits from screening, others will be harmed. This fact has led many physicians to advocate that shared decision-making be used more widely to integrate patients' preferences and values with the decision to accept or decline a screening test.

How often do physicians take the time to explain the harms of cancer screening to their patients? A 2013 research letter published in JAMA Internal Medicine explored this question in an online survey of 317 U.S. adults between 50 and 69 years of age. 83 percent of participants had attended at least 1 routine cancer screening; 27 percent had undergone 3 or more. However, less than 10 percent of participants had ever been informed by their physicians of the risk that the screening test(s) could lead to overdiagnosis and overtreatment. The few physicians who did attempt to quantify this risk generally provided information that was inconsistent with the medical literature.

If the results of this survey are representative of the practices of U.S. primary care clinicians, then more than 90 percent aren't telling patients that there are downsides to undergoing routine mammograms, colonoscopies, and Pap smears. Why not? Is it because they aren't familiar enough with the data to accurately describe these harms? Or is it because they fear that patients who receive information about cancer screening harms will choose to decline these tests?

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This post originally appeared on Common Sense Family Doctor on November 3, 2013.