Colorectal cancer despite colonoscopy: Significant differences depending on the quality of the examination

From the age of 50, it is recommended for everyone in Germany: early detection of colorectal cancer. During a so-called colonoscopy, a thin tube with a camera is inserted through the anus into the rectum. The attending physician can then examine the bowel for precancerous lesions and remove them immediately.

Varying protection against colorectal cancer

To classify doctors according to colonoscopy quality, the researchers first calculated a common quality measure, namely the so-called detection rate. They then compared the occurrence of colorectal cancer over 13 years in three groups of people:

A) people who had a high-quality screening colonoscopy

B) individuals with a lower-quality screening colonoscopy, and

C) individuals without a screening colonoscopy.

In total, they included more than 300,000 individuals in the analyses. “The good news is that even a lower-quality colonoscopy reduces the risk of colorectal cancer compared to people who have not had a colonoscopy. However, the preventive effect is about a third stronger with a high-quality colonoscopy,” explains Dr. Sarina Schwarz, lead author of the study and head of the Translational Cancer Epidemiology Group at BIPS.

Quality of colonoscopies should remain in focus

In Germany, colonoscopies have been subject to a quality assurance program since 2002. Among other things, this program regulates that only experienced physicians from certain specialties may perform colonoscopies.

An earlier study by the team from 2023 (International Journal of Cancer) showed that the detection rate improved over time: While in 2008, about one-third of doctors were in the lowest category for detection rate, by 2017, it was only about one-quarter. “The quality of colonoscopy in Germany has certainly improved over the last two decades. Nevertheless, there is still room for improvement in some areas,” emphasizes gastroenterologist PD Dr. med. Christian Pox, chief physician at the Medical Clinic at St. Joseph-Stift in Bremen and co-author of the study.

“Our results illustrate the importance of the quality of a colonoscopy for the prevention of colorectal cancer. In a next step, we want to investigate whether the quality can be improved by an online course for physicians. This course showed very good results in a US study,” says Prof. Dr. Ulrike Haug, head of the Clinical Epidemiology Department at BIPS and last author of the study. However, she feels it is important to add: “Our results should not unsettle those willing to take preventive measures. Even a colonoscopy of inferior quality is better than none at all!”

What is new?

The 2023 study was the first to show for Germany that there is a correlation between the detection rate of doctors and the occurrence of colorectal cancer after a colonoscopy. In the current study, the researchers compared the preventive effect of screening colonoscopies of different quality with no screening colonoscopy. For this purpose, they used the GePaRD health insurance database, which covers 20 percent of the German population and provides the long observation period required for these studies. The study design they chose minimized the risk of bias that sometimes occurs in observational studies.

Original publications

Schwarz S, Braitmaier M, Pox C, Kollhorst B, Didelez V, Haug U. 13-year colorectal cancer risk after lower-quality, higher-quality and no screening colonoscopy: A cohort study. Journal of Clinical Epidemiology. 2024.

Schwarz S, Hornschuch M, Pox C, Haug U. Polyp detection rate and cumulative incidence of post-colonoscopy colorectal cancer in Germany. International Journal of Cancer. 2023 Apr 15;152(8):1547-1555.

Scientific contact

Prof. Dr. Ulrike Haug, Head of Department Clinical Epidemiology

haug(at)leibniz-bips.de; Tel: +49 (0)421 218-56862

BIPS – Health research for the benefit of people

The population is at the center of our research. As an epidemiological research institute, we see our mission in identifying the causes of health disorders and developing new concepts for the prevention of diseases. Our research provides a basis for societal decisions. It informs the population about health risks and contributes to a healthy living environment.

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