Strategic Communication and Public Relations

Studies underestimate the benefit of lower gastrointestinal endoscopy

No. 44 | 13/09/2013 | by Koh

Precancerous lesions of colorectal cancer can be detected and safely removed through a procedure called lower gastrointestinal (GI) endoscopy, making this measure very effective in cancer prevention. Researchers are currently trying to determine how many colorectal cancer cases and deaths are actually being prevented by endoscopic screening. Scientists from the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) have calculated that its benefit is much higher than study results have suggested so far.


Randomized controlled trials are considered to be the gold standard for evaluating new therapies as well as proving the effectiveness of screening exams. In this type of study, participants are randomly assigned to an experimental group or a control group. The evaluation includes all participants.

However, when the purpose is to discover the value of screening exams such as lower GI endoscopy, a problem arises: participants in an experimental group frequently do not undergo the procedure. On the other hand, participants from the control group may do so outside the study protocol – if for example, they have a health concern.

“This means that the difference between experimental and control groups is diluted, making the protective effect of endoscopic gastrointestinal screening appear smaller than it actually is,” says Professor Hermann Brenner from the German Cancer Research Center. Brenner’s team at DKFZ has now carried out calculations to quantify the amount by which this effect is likely underestimated. The team based their calculations on data from four completed randomized trials on the effectiveness of an endoscopic examination called flexible sigmoidoscopy.

The actual participation rates in from members of the experimental groups were generally 70 percent or even lower. On the other hand, during the relevant period, up to 50 percent of participants from the control groups underwent lower gastrointestinal endoscopy outside the screening programs.

Under these conditions, if lower gastrointestinal endoscopy were 70 percent effective in coping with the incidence and mortality of colorectal cancer, the usual study evaluation method would reduce that figure to approximately 38 percent. If the procedure prevented the incidence of cancer cases by 50 percent, the result in the standard evaluation would be a much less convincing 23 percent.

“Randomized controlled trials do provide information about the effect that screening programs have on the colorectal cancer incidence in the whole population that is offered the examination,” Hermann Brenner says. “However, when considering the protective effect of examinations that have actually been conducted, the rate is much higher and should be correctly communicated in colorectal cancer screening consultations.”

Brenner expects even greater discrepancies to emerge during ongoing studies with a focus on full colonoscopies, because participation rates in the experimental groups are yet lower and, at the same time, the proportion of people in the relevant age group who receive lower gastrointestinal endoscopy outside screening programs continues to rise.

Hermann Brenner, Christian Stock, Michael Hoffmeister: In the era of widespread endoscopy use, randomized trials may strongly underestimate the effects of colorectal cancer screening. Journal of Clinical Epidemiology 2013, DOI: 10.1016/j.jclinepi.2013.05.008

The German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) with its more than 3,000 employees is the largest biomedical research institution in Germany. More than 1,300 scientists at the DKFZ investigate how cancer develops, identify cancer risk factors and search for new strategies to prevent people from developing cancer. They are developing new methods to diagnose tumors more precisely and treat cancer patients more successfully. The DKFZ's Cancer Information Service (KID) provides patients, interested citizens and experts with individual answers to all questions on cancer.

Jointly with partners from the university hospitals, the DKFZ operates the National Center for Tumor Diseases (NCT) in Heidelberg and Dresden, and the Hopp Children's Tumour Center KiTZ in Heidelberg. In the German Consortium for Translational Cancer Research (DKTK), one of the six German Centers for Health Research, the DKFZ maintains translational centers at seven university partner locations. NCT and DKTK sites combine excellent university medicine with the high-profile research of the DKFZ. They contribute to the endeavor of transferring promising approaches from cancer research to the clinic and thus improving the chances of cancer patients.

The DKFZ is 90 percent financed by the Federal Ministry of Education and Research and 10 percent by the state of Baden-Württemberg. The DKFZ is a member of the Helmholtz Association of German Research Centers.


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