A specific type of gut bacteria may be associated with an increased risk of developing bowel cancer, according to new research being presented today (4 November 2019).
Dr Kaitlin Wade, from the University of Bristol, England, will tell the 2019 NCRI Cancer Conference, in Glasgow, how they used Mendelian randomisation to investigate the causal role played by bacteria in the development of bowel cancer.
They found evidence that the presence of an unclassified type of bacteria from the Bacteroidales group increased the risk of bowel cancer by between 2% and 15%.
Dr Wade said their findings support previous studies that have demonstrated that Bacteroidales bacteria are more likely to be present, and in larger quantities, in individuals with bowel cancer compared to those without the disease.
Dr Wade said the research was carried out to see if variation in the human gut microbiome can have an impact on bowel cancer.
While there are studies in mice and humans that have shown an association between the gut microbiome and bowel cancer, few have provided convincing evidence for causality. Mendelian randomisation uses complex statistical analysis of data from large populations to provide evidence for cause and effect, rather than just the existence of an association.
Dr Wade said: “With Mendelian randomisation, we use people’s natural, randomly inherited genetic variations, which alter levels of bacteria within the gut microbiome in a way that mimics a randomised trial, to see whether people with a different genetic makeup, and therefore different gut microbiome profiles, have a different risk of colorectal cancer.
“In this way, we don’t have to edit anyone’s gut microbiome directly by giving antibiotics or probiotics in a randomised trial or waste time waiting to see whether people within the population get colorectal cancer. We just need studies that have already got this information measured.”
The study used data from 3,890 participants in the Flemish Gut Flora Project, the German Food Chain Plus study and the PopGen study, and 120,328 people in the international Genetics and Epidemiology of Colorectal Cancer Consortium.
It found that genetic variation in particular parts of the genome were linked to the presence or varying amounts of 13 types of gut bacteria, and that people with an unclassified type of bacteria from the Bacteroidales group had a higher risk of bowel cancer compared to people who did not have these bacteria.
Dr Wade said further research was needed so that the implications for human health could be fully understood.
“We need to classify the exact species or strain of bacteria in the Bacteroidales group, and we need to do more work to understand how and why human genetic variation can alter the gut microbiome,” she said.
“Even if these results show that these bacteria may cause bowel cancer, we don’t know whether trying to alter them in an effort to reduce the risk of bowel cancer might have other, unforeseen effects on other aspects of health.”
Abstract no: Poster 2532, poster board number 36, area 2. Exploring the causal role of the human gut microbiome on colorectal cancer: application of Mendelian randomization.
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