In search of the tumours’ bacteria
There is a connection between the gut microbiome and colorectal cancer. The question is what it looks like, and how it can be used to tackle the disease.
Text: Annika Lund, in translation from Swedish. First published in the magazine Medicinsk Vetenskap no 3/2026.
The gut contains vast numbers of bacteria, far outnumbering the endogenous cells. The gut microbiome is important for health in many ways, not least because it influences our immune system.
When it comes to the role gut microbiome play in colorectal cancer, so-called fusobacteria have attracted considerable attention. More than a decade ago, it was demonstrated that fusobacteria, which are normally found in the mouth, can end up in the wrong place. They can migrate to the gut and promote the development of colorectal cancer there.
“Since then, our knowledge has advanced. We now know that fusobacteria play a role in tumour growth, the development of metastases and resistance to chemotherapy in colorectal cancer,” says Eduardo J. Villablanca, Professor of Gastrointestinal Immunologi at the Department of Medicine, Solna, Karolinska Institutet.
Mapping gene activity in tissue
Yet fusobacteria are still just one form of bacteria within our extraordinarily diverse gut microbiome.
“We want to have a more open-ended approach to understanding the role of the gut microbiome in colorectal cancer. Our goal is to construct a more complete picture of bacterial presence and tumour interactions in colorectal cancer,” says Eduardo J. Villablanca.
To help them reach their goal, his research group is using an advanced technique that makes it possible to map gene activity in tissue, whether it occurs in the body's own cells or in bacteria. Using this technology, the researchers will examine colorectal cancer biopsies from different patients, with different types of cancer and at different stages. This will provide a wealth of snapshots of the interplay between bacteria and tumour development.
A great deal of valuable knowledge could emerge from this work. One thing they hope for is that it will reveal whether, and if so which, bacteria interfere with particular medical treatments. Such insights could lead to more effective use of medicines.
And yes, it is possible that fusobacteria will prove to play a decisive role. Hypothetically, researchers might then have identified a weak spot in tumour development, similar to how an HPV infection is central to the development of cervical cancer. In the latter case, vaccination against HPV has made the goal of eradicating cervical cancer a realistic one.
However, many pieces of the puzzle still need to fall into place before any such vision becomes attainable for bowel cancer, says Eduardo J. Villablanca.
“Even so, I would argue that we are moving in that direction,” he says.
How to care for your gut microbiome
Fibre-rich foods, such as vegetables, legumes and wholegrains, provide nourishment for beneficial gut bacteria, known as prebiotics. It is also beneficial to introduce new beneficial bacteria, known as probiotics, which can be found in fermented foods.
Source: Eduardo J. Villablanca