The Harms of Screening

Abstract

AMERICANS ARE ENTHUSIASTIC ABOUT SCREENING, ESpecially cancer screening. What could be wrong with screening, especially if it can detect a lifethreatening condition at an earlier stage? Trials show that early detection of breast, colorectal, and other cancers can reduce cause-specific mortality rates, and the same could apply to other conditions. With presumably little to lose and much to gain from early detection, why recommend against screening unless the concern is costs? Are lives being lost to save money? But costs are rarely the reason that guidelines set limits on screening. Most screening controversies turn on how to balance potential harms relative to potential benefits. Harms from screening programs are real; the burden of these harms can be disputed, but their existence cannot. Screening can produce iatrogenic complications (eg, perforation from colonoscopy), anxiety over abnormal results, and a cascade of follow-up tests and treatments. Screening can also precipitate overdiagnosis, the workup and treatment of conditions that qualify as disease but pose little threat to patients’ health. Concerns about the harms of screening might seem exaggerated without closer scrutiny. For instance, if a test with 90% sensitivity and 96% specificity (better than most screening tests) is used to screen for a condition with a prevalence of 0.6% (typical of some cancers), 88% of abnormal results will be erroneous; for every 1000 patients screened, only 6 will have the condition and 40 will have falsepositive results. That ratio may be acceptable if the benefits obtained by the 6 patients with true disease outweigh the harms incurred by the 1000 patients who undergo screening, but what if there is little evidence that early detection improves their prognosis? If only 1 or 2 of the 6 patients obtain benefit, is it ethical to subject the entire population to screening? The concern about overdiagnosis is justified: by some estimates, overdiagnosis accounts for 15% to 25% of screen-detected lung cancers and potentially more breast and prostate cancers. Whether the harms are important enough to limit screening has been a vociferous debate for decades. In the 1980s, the most cautious groups—notably the US Preventive Services Task Force (USPSTF)—broke sharply with proponents of screening. Skeptics argued that the potential harms made it unethical to recommend screening without compelling scientific evidence of meaningful benefits (eg, lower morbidity/mortality). The proponents (eg, American Cancer Society, American College of Radiology) dismissed concerns about harms and warned that waiting for definitive evidence would cost lives. In the 1990s, the opposing parties found middle ground as both the science and respect for harms became stronger. In 1992, citing mounting evidence of benefits, the USPSTF abandoned its earlier skepticism and endorsed fecal and sigmoidoscopy screening for colorectal cancer. In 2000 and 2001, respectively, the American Urological Association and American Cancer Society recommended that men obtain information about harms before undergoing prostatespecific antigen (PSA) screening. In 2002, the USPSTF added colonoscopy as a screening option and abandoned its opposition to mammography screening for women 40 years and older. However, a largely unnoticed caveat in the 2002 mammography guideline revealed continuing concern about harms: “The precise age at which the benefits from screening mammography justify the potential harms is a subjective judgment and should take into account patient preferences. Clinicians should inform women about the potential benefits . . . , potential harms . . . , and limitations . . . that apply to women their age.” In 2008, the apparent consensus in guidelines began to unravel. Two colorectal cancer screening tests that the USPSTF found lacking in evidence—fecal DNA testing and computerized tomographic colonography—were endorsed by the American Cancer Society and medical specialty societies. In 2009, the USPSTF issued a controversial recommendation against “routine” mammography among women aged 40 to 49 years. Amplifying its earlier caveat, the USPSTF urged women of this age group to first make an informed decision with their physician that considered individual clinical context and “the patient’s values regarding specific benefits and harms.” In 2011, concern about