The findings, published in the Journal of the National Cancer Institute​, come from one of the largest epidemiological studies of human gut bacteria and colorectal cancer ever conducted, and show that a decreased bacterial diversity in the gut is associated with colorectal cancer risk after adjusting for age, sex, BMI, race, and smoking.

Led by Dr Jiyoung Ahn from New York University School of Medicine, the team compared the DNA composition of intestinal microbes in the stool samples of 141 colorectal cancer patients and healthy volunteers - finding that samples from colorectal cancer patients had fewer beneficial bacteria and more harmful bacteria than people without the disease.

The team noted that due to the potentially modifiable nature of the gut bacteria, the findings may have implications for cancer prevention.

"Identification of these microbes may open the door for colorectal cancer prevention and treatment,"​ said Ahn. "Our next step is to study how diet and lifestyle factors modulate these gut bacteria associated with colorectal cancer. This may lead to ways to prevent this disease."​

Study details​

The team extracted DNA from fecal samples of 47 case subjects and 94 sex- and body mass index-matched control subjects. The samples were sequenced to determine the gut microbial community structure of case vs control subjects - with the authors finding several trends in abundance ofckey bacteria in the fecal samples.

Participants with colorectal cancer showed decreased levels of Clostridia, which include some bacterial family members that ferment dietary fiber, to butyrate - which is a major colonic metabolite that may inhibit inflammation and carcinogenesis in the colon.

In addition increased levels of Fusobacterium and Porphyromonas - both of which are bacteria related to inflammation in the mouth and gastrointestinal track was observed for cancer patients vs control subjects.

In an accompanying editorial (found here​) Drs Volker Mai, and J. Glenn Morris, Jr., from the University of Florida at Gainesville FL, commented tgar the findings by Ahn and colleagues are exciting. However, they also noted: "CRC occurrence is known to be influenced by host genetics, as well as factors such as obesity, nutrition and exercise; given that these factors also influence microbiota, separation of cause and effect among all of these factors may become quite difficult."​

Mai and Morris therefore suggested that prospective cohort studies are warranted.

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Source: Journal of the National Cancer Institute​

Published online ahead of print, doi: 10.1093/jnci/djt300​

"Human Gut Microbiome and Risk of Colorectal Cancer"

Authors: Jiyoung Ahn, Rashmi Sinha, et al​