Colorectal cancer continues to be one of the most common forms of oncology in Western countries and a significant cause of cancer-related mortality.
Although age, diet, and lifestyle influence risk, the exact causes of colorectal cancer are still not fully understood. In recent years, researchers have been particularly focused on the gut microbiome — a vast system of bacteria, viruses, and other microorganisms that inhabit the digestive tract.
Recently, researchers from the University of Southern Denmark and Odense University Hospital discovered a previously unknown virus residing within the common gut bacterium Bacteroides fragilis. It turned out that this virus is significantly more prevalent in people suffering from colorectal cancer.
The bacterium Bacteroides fragilis has long raised many questions within the scientific community. It has already been linked to bowel cancer; however, it is also present in most healthy individuals, which seemed paradoxical: why does a common component of the microbiome sometimes associate with disease?
The answer may lie not in the bacterium itself, but in the virus it carries. Scientists found that in patients who were later diagnosed with colorectal cancer, Bacteroides fragilis more frequently contained a specific bacteriophage — a virus that infects bacteria. Researchers emphasize that at this stage, this discovery does not prove that the virus directly causes cancer. It may participate in the disease's development, or simply signal changes that have occurred in the gut.
This signal was first detected by scientists in Danish data. They analyzed patients with severe blood infections caused by Bacteroides fragilis, comparing bacterial samples from those who later received a colorectal cancer diagnosis to those who did not become ill.
This finding was then validated on a much larger sample, including stool samples from 877 individuals from Europe, the USA, and Asia. The picture was fully confirmed: in people with colorectal cancer, these viruses were found about twice as often.
In the future, such viral markers could potentially help assess the risk of colorectal cancer through stool analysis. Initial data suggest that some of them may indicate approximately 40% of cancer cases, while they are absent in most healthy individuals.
However, this work is still at a very early stage of development. Scientists still need to determine in detail how the virus affects the behavior of the bacterium and whether it can indeed participate in the disease's development.
