In hoeverre is kanker screening wenselijk of schadelijk?
"Whether it is prostate-specific antigen, mammography, or colorectal cancer screening, there is plenty of uncertainty about the magnitude of both the benefits and the harms," he wrote. "So, we will need to think in terms of giving patients plausible ranges -- not single numbers -- to express the benefits and harms of cancer screening."
October 22, 2013 -- Patients are not being told about the possibility of overdiagnosis and overtreatment as a result of cancer screening programs, and many say they wouldn't start a screening program if the overdiagnosis rate is too high, according to research published online in JAMA Internal Medicine.
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Although cancer screening can find treatable disease at an earlier stage, it can also detect cancers that will never progress, leading to unnecessary surgery, chemotherapy, and radiation, wrote Odette Wegwarth, PhD, and colleague Gerd Gigerenzer, PhD, of the Max Planck Institute for Human Development in Berlin.
"The consequence of overdiagnosis is overtreatment ... that provides the patient no benefits, but only adverse affects," Wegwarth and Gigerenzer wrote. "For instance, for every 2,000 women attending mammography screening throughout 10 years, one less dies of breast cancer. Concurrently, approximately 10 women with pseudodisease receive a diagnosis of breast cancer and are unnecessarily treated."
Wegwarth and Gigerenzer conducted an online survey of 317 U.S. men and women ages 50 to 69 years to find out how many patients had been informed of overdiagnosis and overtreatment by their physicians and how much overdiagnosis they would tolerate when deciding whether to start or continue screening. The survey sample came from the U.S. panel of Survey Sampling International in December 2010. Only people who had no cancer history and who had been invited to undergo screening by their physicians in the past were included (JAMA IM, October 21, 2013).
Of the survey participants, 52.4% were women, 60.6% were between the ages of 50 and 59, 84.9% were white, and 64% had high school or some college education.
The participants reported the following regarding screening:
- 19.9% had attended one routine cancer screening
- 36% had attended two routine cancer screenings
- 27.1% had attended three or more
- 17% had never been screened for cancer
Mammography was the most common cancer screening exam reported by women, and colonoscopy/sigmoidoscopy and prostate-specific antigen (PSA) testing were the most common exams reported by men, Wegwarth and Gigerenzer wrote.
The survey showed that only 30 survey participants, or 9.5%, said their physician had discussed the possibility of overdiagnosis and overtreatment in cancer screening. Of these 30, nine said that their physician quantified the risk of overdiagnosis. However, the ranges that survey participants provided were either overestimates or underestimates of the risk, according to the authors.
Fifty-one percent of the participants said they would not start a screening protocol that resulted in more than one overtreated person per one life saved from cancer death, they wrote. But 58.9% said they would continue to be screened once they had started, even if they learned that the protocol resulted in 10 overtreated people per one life saved.
One of the most startling findings was that 69% of the participants indicated they would not start screening if overdiagnosis rates were more than 10 cases per one life saved, according to Wegwarth and Gigerenzer.
"The results of the present study indicate that physicians' counseling on screening does not meet patients' standards," they wrote. "Most individuals desired information about screening harms, which was not given, and attested that this knowledge would matter to them."
In a commentary also published on October 21, Dr. H. Gilbert Welch, from the Dartmouth Institute for Health Policy and Clinical Practice, wrote that Wegwarth and Gigerenzer's survey illuminates how Americans feel about screening when given the context of overdiagnosis.
"Millions of Americans might not choose to be screened if they knew the whole story; however, most do not," Welch wrote. While many patients understand there are benefits and harms to treatment, they are not taught the same regarding screening. "There are benefit and harms to consider in screening -- just as there are in treatment."
There are many questions about the survey to consider, Welch conceded, including whether the sample was representative of the U.S. population in that age range, how well the survey participants understood the numbers, and whether the survey overemphasized the harms of overdiagnosis and overtreatment while underemphasizing the benefit of avoiding cancer death.
Researchers need to investigate how patients can best understand the trade-offs of cancer screening. However, consensus first needs to be reached about what the benefit and harm numbers actually are, Welch concluded.