Examining Gut Bacteria May Improve Colon Cancer Screening

Analyzing the spectrum of gut bacteria found in a stool sample improved a colorectal cancer and pre-cancerous polyp screening test five-fold when compared to a fecal occult blood test (FOBT), according to the results of a study published in Cancer Prevention Research.  

Analysis of gut bacteria in stool samples improved detection of colon cancer or precancerous polyps by five times compared with a standard fecal occult blood test (FOBT) and risk factors, investigators reported. The added examination improved the ability of researchers to tell the difference between those with invasive colorectal cancer, those with pre-canceroups polyps, and healthy individuals.

According to Patrick D. Schloss, PhD, associate professor in microbiology and immunology at the University of Michigan in Ann Arbor and colleagues, the study results “demonstrate the feasibility of using the composition of the gut microbiome to detect the presence of precancerous and cancerous lesions.”

The microbe test increased the probability of detecting an adenoma (polyp) by 4.5-fold compared to the FOTB when clinical risk factors such as age and race were added (P=.002). The test, likewise, increased the probability of detection of a carcinoma by 5.4 times when clinical risk factors for colorectal cancer-age, race, body mass index-were added.

“We found that the composition of the gut microbiome allowed us to identify who in our study had precancerous adenomatous polyps and who had invasive colorectal cancer,” said Schloss in a statement. “If our results are confirmed in larger groups of people, adding gut microbiome analysis to other fecal tests may provide an improved, noninvasive way to screen for colorectal cancer.”

The FOBT is a commonly used non-invasive test for colorectal cancer which detects blood in the stool. However, because blood in the stool is an indication not only of a carcinoma or adenoma, but also other gut disorders, improvements of this test to decrease false-positive results are needed. Although the specificity of the test is between 87% and 98% based on prior studies, the sensitivity is only about 9% to 12%.

Using a microbe biomarker in conjunction with known clinical risk factors of colorectal cancer, the researchers analyzed stool samples from 30 healthy individuals, 30 patients with pre-cancerous adenomatous polyps, and 30 patients with invasive colorectal cancer to identify differences in microbiome profiles of these three groups.

The researchers sequenced the DNA of the gut bacteria and classified the sequences into clusters called operational taxonomic units (OTUs). Specific OTUs from different bacteria were either more or less abundant among patients with polyps compared to health individuals-five different OTUs were in higher abundance among patients with polyps while seven different bacterial OTUs were in lower abundance compared to healthy subjects. A different set of OTUs was either in higher or lower abundance in healthy individuals compared to those with colorectal cancer.

According to the authors, the analysis suggests that colorectal cancer is likely to be a polymicrobial disease. While certain bacterial pathogens may contribute to tumor formation in the colon, based on these and prior results, it is likely that a lack of certain bacterial strains, as demonstrated in this study, could also play a role in colorectal cancer.

Analyzing these gut microbe signatures was better than FOTB in telling the difference between an individual with a pre-cancerous polyp and one with colorectal cancer. Adding factors such as FOTB results and BMI improved this distinction according to the study.

The goal of the new approach, according to Schloss, is to complement standard colorectal screening, which could be a new tool in non-invasive screening.

Still, the current study is a validation of the use of microbe markers to identify colorectal cancer and polyps in patients, but does not yet implicate any specific bacteria is facilitating or causing cancer or polyps in the gut.