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Why do colon polyps become cancerous?

A recent study has explored how the composition of gut microbiota contributes to colorectal polyps becoming cancerous.

Any cancer that affects the colon and rectum is referred to as colorectal cancer. The colon and the rectum make up the large intestine, which is part of the gastrointestinal system. The colon absorbs water and salt from food matter after it has passed through the small intestine. Then, the remaining waste matter travels to the rectum, where it is stored until it passes through the anus.

Colon cancer and rectal cancer are often grouped together because they have numerous features in common. Colon cancer can start anywhere in the colon, which is about 5 feet long, whereas rectal cancer begins in the rectum, which is just the last 5 inches of the colon. Most colorectal cancers starts as polyps, which are small clumps of cells that form within the inner lining of the colon or rectum. However, not all polyps become cancerous. The chance of a polyp turning into cancer depends on several factors, including the type, size and frequency of the polyps.

Studying colorectal polyps

Colorectal cancer is a major health concern worldwide and there is growing evidence to support that the gut microbiota may play a significant role in the initiation of the disease. However, little is known about the how the composition of microbiota is linked with pre-cancerous polyps.

A recent study, conducted by researchers at the University of Washington School of Medicine and published in Cell Host & Microbe, has uncovered distinct microbial signatures between patients with and without colorectal polyps using sequencing and culturing techniques.

In total, forty patients were tracked after undergoing routine colonoscopies and biopsies of colorectal polyps. An increased presence of a common gut bacteria, called Bacteroides fragilis, in mucosal biopsies was found to indicate a higher risk of colon polyps becoming cancerous. Moreover, B. fragilis in patients with polyps often induced an inflammatory response and was enriched in genes associated with lipopolysaccharide biosynthesis.

Exploring colorectal cancer risk

This research has revealed that B. fragilis differs in its ability to induce inflammation between patients with colon polyps and without. It provides important insights into the microbial microenvironment of colorectal polyps and explores key genomic differences between relevant bacterial strains.

William DePaolo, an Associate Professor who worked on this project, said:

“The whole idea is that most people look at advanced colorectal cancer and think of the microbiome, but it’s hard to determine if the microbiome has changed and when it changed. So, we took an earlier look at the disease and asked when the microbiome might be pushing a polyp toward cancer. What our data suggests is that, to survive within an environment where metabolic and inflammatory changes are occurring, a normally healthy gut and related bacteria may adapt in such a way that causes it to contribute to the inflammation rather than suppress it.” 

New screenings for colorectal cancer could search for the strain of B. fragilis that is now suspected to induce inflammation. In theory, these investigations into gut bacteria should be done prior to the colon polyps developing. Nevertheless, the next step is to expand this study to around 200 participants, to determine whether a faecal sample could be used instead of a colorectal biopsy. In turn, this will make the procedure as easy and simple as possible and as a result drive the rates of colorectal cancer down.

Image credit: healthessentials

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Cancer Research / Colon Cancer / Microbiome