Knowing the warning signs of bowel cancer can make a real difference, especially because early detection improves treatment outcomes. But researchers are also looking at another clue: what is happening inside the gut microbiome.
A new study suggests that certain viruses found inside a common gut bacterium may be linked with higher bowel cancer risk. The research does not prove cause and effect, but it adds to growing interest in how the gut microbiome may influence cancer risk over time.
Bowel cancer, also called colorectal cancer, is one of the most common cancers globally and a leading cause of cancer deaths worldwide. The study, published in Communications Medicine, focused on a feature often seen in bowel cancer research: dysbiosis, an imbalance in the gut microbiome, the community of bacteria and viruses that live in the intestines.
Because the microbiome is complex, researchers often struggle to identify which changes matter most. For this study, they focused on a bacterium commonly found in both healthy people and people with bowel cancer, Bacteroides fragilis, to see whether there were meaningful differences.
Researchers analysed bacteria taken from people with and without bowel cancer, looking closely at genetic patterns. In samples from people with bowel cancer, they identified two previously unknown viruses inside Bacteroides fragilis.
They then checked stool samples from hundreds of people with and without bowel cancer to see whether the same viruses showed up more often in one group.
“These viruses were found much more often in people with colorectal cancer than in people without it,” radiation oncologist Dr Michael Chuong explains. People with bowel cancer were almost twice as likely to have these virus-infected bacteria.
Dr Chuong stresses that the findings do not mean viruses in general cause bowel cancer. But the discovery may still be useful. “The viruses may change how the bacteria behave,” Dr Chuong says. “While we don’t yet know if they directly cause cancer, their presence could help doctors identify people at higher risk.”
The research remains early and it will take more studies before this kind of testing could play a role in routine screening or prevention. For now, the strongest tools for reducing risk and improving outcomes still include recognised screening pathways, paying attention to symptoms and speaking with a GP if anything feels unusual or persistent.
How to lower your chances of colon cancer
Bowel cancer links with several lifestyle factors that you can influence, which matters even more if you have a family history. Dr Chuong says the most practical steps include:
- Keep up with screening when you are eligible, including colonoscopy or stool tests
- Eat a higher-fibre diet with plenty of fruit, vegetables and wholegrains
- Limit red and processed meat
- Move regularly with exercise you can stick with
- Maintain a healthy weight
- Avoid smoking
- Limit alcohol
The bottom line
“This study suggests that the interaction between bacteria and viruses in the gut may play a role in the risk of colorectal cancer,” says Dr Chuong. “In the future, testing for these viruses in stool samples could potentially help detect cancer earlier or improve screening tests. However, more research is needed before this becomes part of routine care.”
For now, screening remains the most effective tool for early detection, alongside lifestyle choices that support gut and overall health.
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