Gut microbes up risk of colorectal cancer

Washington – A new study has found that the risk of colorectal cancer may well be hidden in the gut microbes.

According to the research, transferring the gut microbes from a mouse with colon tumors to germ-free mice makes those mice prone to getting tumors as well.

“We know that humans have a number of different community structures in the gut. When you think about it, maybe different people – independent of their genetics – might be predisposed,” study author Joseph Zackular of the University of Michigan, said.

Scientists have known for years that inflammation plays a role in the development of colorectal cancer, but this new information indicates that interactions between inflammation and subsequent changes in the gut microbiota create the conditions that result in colon tumors.

Co-author Patrick Schloss, also of the University of Michigan, was somewhat surprised by the clarity of the results.

“We saw more than two times the number of tumors in mice that received the cancerous community [than in mice that received a healthy gut community],” Schloss said.

“That convinced us that it is the community that is driving tumorigenesis. It’s not just the microbiome, it’s not just the inflammation, it’s both,” he said.

Known risk factors for developing colorectal cancer include consuming a diet rich in red meat, alcohol consumption, and chronic inflammation in the gastrointestinal tract (patients with inflammatory bowel diseases, such as ulcerative colitis, are at a greater risk of developing colorectal cancer, for instance).

Cancer patients also exhibit shifts in the composition of their gut microbiota – a phenomenon called dysbiosis – but it’s unclear whether changes in the microbiome drive the development of cancer or the cancer drives changes in the microbiome.

The study is published in mBio, the online open-access journal of the American Society for Microbiology.