May 6, 2026, 2:42 pm | Read time: 5 minutes
A long-term study has examined how a colonoscopy affects the risk of colon cancer and the mortality risk in the event of a colon cancer diagnosis over the long term. The results are surprising.
Colon cancer is one of the most common cancers in Germany. According to the Center for Cancer Registry Data, around 30,000 men and nearly 25,000 women are diagnosed with it annually.1 Starting in April 2025, men and women with statutory health insurance in Germany can have a colonoscopy (colonoscopy) twice, ten years apart, starting at age 50.2 This serves as a preventive measure against colon cancer. During this procedure, polyps that could develop into cancer can also be removed. If the findings are unremarkable, another colonoscopy—also called screening—can be performed after ten years. Norwegian researchers have now conducted a large long-term study to investigate how a colonoscopy affects the risk of colon cancer.3
What Is the Impact of Colon Cancer Screening?
As part of a multinational, population-based randomized controlled trial, Norwegian researchers evaluated health and mortality data from 84,583 men and women. At the start of the study, participants were between 55 and 64 years old. The subjects came from Norway, Poland, and Sweden.
At the beginning of the long-term study, participants were randomly assigned in a 1:2 ratio to either a preventive colonoscopy or no screening. The researchers aimed to determine how a one-time colon cancer screening affects the risk of colon cancer and mortality after ten to fifteen years. The first data evaluation was conducted after ten years, and now the results after thirteen years are available.
This Is What the Data Shows
The evaluation of health and mortality data after 13 years has revealed the following insights:
- In the group of participants who underwent colon cancer screening (28,217 people received an invitation, 42 percent underwent the colonoscopy), there were 375 cases of colon cancer over 13 years. This accounts for 1.46 percent of the participants (including those who did not undergo the screening despite the invitation).
- In contrast, 912 participants in the non-screening group developed colon cancer, with the group consisting of 56,366 people. This represents 1.8 percent of the participants compared to 1.46 percent in the screening group.
- The risk of malignant colon cancer was 0.51 percent in the screening group compared to 0.56 percent in the non-screening group.
- For men, the colon cancer risk in the screening group was significantly lower at 1.69 percent compared to 2.19 percent in the non-screening group.
- For women, the difference was smaller, with 1.24 percent (screening group) compared to 1.43 percent (non-screening group).
- The mortality rate from colon cancer was 0.41 percent in the screening group and 0.47 percent in the non-screening group.
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How Do the Somewhat Surprising Results Come About?
In summary, this study shows that colonoscopy significantly reduced the risk of developing colon cancer. However, the impact on mortality from colon cancer was less clear than expected. In the screening group, the mortality risk from colon cancer was 0.41 percent, while it was 0.47 percent in the non-screening group. This was significantly lower than the researchers had anticipated at the time of the study’s design, which was 0.82 percent.
However, one of the study’s lead authors, Dr. Michael Bretthauer from the University of Oslo, has an explanation, as he explained to the professional portal “MedpageToday“: “We know from cancer statistics that survival rates for colon cancer patients are significantly higher today than they were ten or even five years ago.” According to him, the chances of survival upon a colon cancer diagnosis are significantly higher today. This is mainly due to much better treatment methods, more advanced surgical procedures, and improved radiation therapy. Additionally, immunotherapy has been available for about five years. “This is all good news for patients,” the study co-author notes. Conversely, this means that the better the therapeutic treatment of colon cancer becomes, the smaller the benefits of a preliminary examination. This could possibly explain the slight advantage of the screening group in terms of mortality risk in the present study.
Men in Particular Benefit from a Colonoscopy
The study also shows that a colonoscopy significantly reduces the risk of colon cancer, especially in men. “We found that colonoscopy is more effective in men than in women… and it is more effective in the lower part of the colon than in the upper part,” adds Dr. Bretthauer. These findings could help assess the usefulness of the examination more individually, such as when recommending colonoscopies for specific target groups. It is now up to the responsible parties, such as health insurance companies, to correctly interpret and learn from these results.
The most significant factors in preventing colon cancer are within our control. By maintaining a healthy lifestyle, such as avoiding smoking, eating a high-fiber diet, consuming little alcohol, maintaining a healthy weight, and exercising regularly, we can significantly reduce the risk of colon cancer.
However, a weakness of the study should be highlighted: The data of participants who did not undergo a colonoscopy despite being invited were not excluded. They were included in the evaluation and may have contributed to the somewhat surprisingly low statistical effects.