How Much Is Too Much Cancer Screening?

Overdetection—when a cancerous lesion is found that would otherwise not have caused any symptoms or early death—is considered the most important adverse effect (AE) of cancer screening, leading to unnecessary tests and treatment. But when do nonclinicians believe detection crosses that threshold?

Researchers from the University of Oxford in the United Kingdom (UK) surveyed 1,000 adults about 3 types of cancer screening: breast, prostate, and bowel. For each type, they presented the absolute number of cases per year in the UK and described the treatment, including AEs. They also presented 2 hypothetical screening scenarios, both of which represented a population of 1,000 adults with a 5% incidence of cancer and 1% cancer-specific mortality. The first scenario represented a 10% reduction of cancer-specific mortality as a result of screening; the second a 50% reduction. All information was presented in written format with absolute numbers and in graphics, to aid understanding. Throughout, the researchers used the term overdetection, rather than overdiagnosis, to avoid confusion with misdiagnosis (something documented in earlier studies).

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Of the survey respondents, 48 had a previous cancer diagnosis and 54% had been screened for cancer at least once.

The researchers found significantly higher screening acceptance rates for the 50% reduction compared with the 10% reduction (P < .001), although, they add, “acceptability of overdetection did not increase 5-fold when benefit increased 5-fold.” Women accepted more overdetection in breast cancer than in bowel cancer; men accepted more overdetection in prostate cancer than in bowel cancer.

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Across all scenarios, 3.5% to 7.4% of people said they would not accept any level of overdetection. By contrast, 7.1% to 13.9% would accept the entire population of 1,000 people being overdetected to avoid 1 or 5 people dying of cancer.

Patient education leaflets rarely discuss overdetection, the researchers noted. Clearly, there is room for more education, and not only for potential patients, but also for health care providers. Evidence suggests, they say, that clinicians have an equally poor understanding of diagnostic accuracy.

Source
Van den Bruel A, Jones C, Yang Y, Oke J, Hewitson P. BMJ. 2015;350:h980.
doi: 10.1136/bmj.h980.