Colorectal cancer remains one of the most common forms of cancer in Western countries and a major cause of mortality in terms of oncological diseases. Although age, diet and lifestyle are well-known risk factors, the exact mechanisms that trigger the disease are, in many cases, still unclear. In this context, researchers pay increasing attention to the intestinal microbiome – the community of bacteria, viruses and other microorganisms in the digestive tract.
Colorectal cancer remains one of the most common forms of cancer. PHOTO: Shutterstock
A study conducted by researchers in Denmark and published in Communications Medicine shows that a newly identified virus, present inside a common intestinal bacterium, occurs more frequently in patients with colorectal cancer. The finding suggests a possible link between viruses that infect bacteria in the gut and the risk of disease.
New virus, found in a common bacteria
The research team from the University of Southern Denmark and Odense University Hospital analyzed the bacteria Bacteroides fragilisassociated for a long time with colorectal cancer, but also present in many healthy people. To understand why this bacterium is linked to disease only in certain cases, researchers investigated what is inside it.
The results showed that in patients who later developed colorectal cancer, Bacteroides fragilis was more commonly infected with a specific virus. The virus, a bacteriophage – meaning a virus that infects bacteria – has not been previously described in the literature and is considered a new type.
Association, not proof of causation
The study highlights a statistical association between the presence of this virus and colorectal cancer, but does not prove that the virus causes the disease. The researchers point out that it is possible that the virus is just a marker of already existing changes in the intestinal environment.
The research is based on data from a large study in Denmark, which included approximately two million people. Patients with severe blood infections caused by Bacteroides fragilis were analyzed, some of whom were diagnosed with colorectal cancer in the following weeks.
Internationally confirmed results
After initial observations, made on a limited number of samples, the hypothesis was tested on larger international data sets. The researchers analyzed stool samples from 877 people in Europe, the United States and Asia, with and without colorectal cancer.
Oncology patients showed traces of these viruses in the intestine about twice as often as compared to healthy people. The association was constantly observed, but without establishing a direct causal relationship.
In preliminary analyses, certain viral sequences allowed the identification of about 40% of colorectal cancer cases, while the majority of healthy people did not present them. However, the results are still in an early experimental phase, and the researchers caution that further studies are needed before these findings have clinical applications.
