Fecal Microbiome Analysis May Help Predict Colon Adenoma Prevalence, Lifetime Risk for Colorectal Cancer

Investigators examined differences in the microbiomes of patients with colorectal neoplasia.

The following article is a part of conference coverage from the American College of Gastroenterology 2021 Annual Meeting , held from October 22 to 27, 2021. The team at Gastroenterology Advisor will be reporting on the latest news and research conducted by leading experts in gastroenterology. Check back for more from ACG 2021.


The fecal microbiome may provide insight into a person’s risk of developing colorectal cancer (CRC) in their lifetime, according to research presented at the American College of Gastroenterology (ACG) 2021 Annual Meeting, held from October 22 to 27, 2021, in Las Vegas, Nevada and virtually.

The study included a prospective cohort of patients aged between 50 and 75 years who were referred for a colonoscopy. In addition to collecting stool samples for microbiome analysis and performance of fecal immunochemical tests (FIT), the investigators also applied the National Cancer Institute (NCI) CRC risk assessment tool to the cohort.

Using the available samples and employed tools, the investigators calculated the microbiome alpha diversity with the Shannon index and assessed individual bacterial and fungal species. Additionally, the researchers compared the microbiomes based on predicted lifetime risk probability for CRC, as derived from the NCI CRC risk assessment tool.

Out of the 34 patients referred for colonoscopy, a total of 10 (29.4%) had ≥1 adenoma, including advanced adenomas (n=2) and sessile serrated adenomas (n=2). In the 2 patients who were FIT-positive, 1 had an advanced adenoma.

According to the investigators, the median predicted lifetime risk for CRC was 2.75%. In the first risk quartile, the prevalence of adenoma was 1.5%, while the prevalence of adenoma in the fourth quartile was 62.5% (P <.001). Measured alpha diversity was slightly higher in patients with vs without adenoma, but the difference wasn’t statistically significant (P =.1).

The investigators found 9 unique species in the group of patients with adenomas. Bacterial species Blautia obeum and Lysinibacillus boronitolerans were increased in relative abundance in patients with adenomas (mean, 0.0002; P =.01 and 0.0007; P =.03, respectively).

The lifetime risk for CRC was significantly associated with Parabacteroides distasonis (P =.05) and nonsignificantly associated with Escherichia hermannii (P =.09). In contrast, there was a negative association with 4 other species (P <.1]. There were no correlations between fungal species and adenoma prevalence or lifetime risk for CRC.

“Given these associations, larger trials are needed to potentially implement further data in the clinical setting,” the investigators concluded.

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Alharfi SA, Cooper G, Ghannoum M, Furey N, Al-shakhshir H. Fecal microbiome associated with both colon adenomas and lifetime colorectal cancer risk. Presented at: ACG 2021 Annual Meeting; October 22-27, 2021; Las Vegas, NV and virtual. Abstract P0262.