Study Findings Show Cancer Screening Trials Seldom Tally Harms

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Cancer Screening Trials Seldom Tally Harm

According to the authors of a ‘quantitative analysis of randomized trials,’ researchers and investigators of cancer-screening trials such as mammography and colonoscopy "seldom quantify the harms" of their efforts.

They point out that the "most important harms,” overdiagnosis and false-positive findings were quantified in only 7% and 4%, respectively, of the 57 cancer-screening trials reviewed.

"We found that the harms were poorly reported," write the authors, led by Bruno Heleno, PhD, a fellow in the Department of Public Health at the University of Copenhagen in Denmark.

The results have gone on to be published online in BMJ.

However, professor of cancer screening at the Wolfson Institute of Preventive Medicine in London, United Kingdom, Stephen Duffy, MD, strongly contends with the study, despite having no direct involvement in it.

"In my view, cancer-screening trialists have, in the main, done their best to describe both positive and negative effects of screening. Furthermore, this paper gives a false impression about the reporting of negative effects," said Duffy.

Duffy continued his criticisms of the study, attacking its faulty accounting.

"Without even looking at the literature, I can think of 4 mammography trials that estimate overdiagnosis, whereas the table in the paper reports only 2," he said.

In retaliation, Heleno noted that the study’s criteria for excluding certain trials were less severe and would "not change the conclusion" about substantial underreporting.

“The benefits of cancer screening were quantified much more often than the harm-related outcomes in trials. For instance, cancer-specific mortality and cancer-specific incidence were each tallied in more than 80% of the trials,” the authors reported.

They went on to argue that “the pluses and minuses of screening should be equally well quantified, because screening typically occurs in healthy people who deserve balanced information.”

Duffy also argued that the authors utilized a "crude" quantitative method to evaluate harms reporting.

The authors used a ruler to measure the amount of physical space and discovered that the average percentage of space designated to harms was only 12%.

The authors examined an array of databases to find trials that assessed cancer screening. They looked, for example, for screening trials for breast cancer with mammography, self exam, or clinical exam; colon cancer with endoscopy or fecal occult blood testing or virtual colonoscopy; and lung cancer with chest x-ray or low-dose spiral computed tomography.

Individual articles were also useful only if they provided data for both the screening and control groups.

They found 57 trials involving 10 different screening interventions and more than 3 million study participants. The trials were then evaluated for the inclusion of 7 different types of harm.

The harms were determined in a low percentage of the trials, with a couple of exceptions: overdiagnosis (7%), false-positive findings (4%), somatic complications (19%), negative psychosocial consequences (9%), invasive procedures (47%), all-cause mortality (60%), and withdrawal because of adverse events (2%).

Yet in order for a specific harm to be considered fully evaluated, a trial must have quantified that specific harm for both the screened and control groups.

However, Duffy criticized the authors’ claim that only 4% of screening trials reported false-positive results, as he drew on his own experience in mammography tria

ls to roughly determine the accuracy of the finding in the larger set of 57 trials.

"All the mammography trials have reported quantitative false-positive results. Therefore, again, the paper is misleading,” commented Duffy.

The authors note that only 4% of trials reported false-positive results for both the screened and control groups, however they recognize that in their study 32% of the 57 trials analyzed provided false-positive information for the screened group alone.

They chose to focus on the 4% finding because they believe that randomized cancer-screening trials should be held to the highest standards.

“Reporting harm outcomes for the intervention and control groups is a central recommendation in the guidelines for reporting randomized trials," they wrote.


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