Oral Microbiome Linked to Site-Specific CRC Risk

TOPLINE: 

While no overall associations emerged between oral microbial characteristics and colorectal cancer (CRC) risk, researchers identified significant site-specific connections. The presence of Olsenella more than doubled the risk for distal colon cancer, while Prevotella 2 increased the risk for rectal cancer by 68%.

METHODOLOGY:

• Oral bacteria detected in feces have been linked to CRC in previous studies, with CRC cases showing greater richness of oral microbes compared to controls.
• Researchers conducted a prospective nested case-cohort study across three United States cohort studies: the Agricultural Health Study, National Institutes of Health-AARP Diet and Health Study, and Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial and compared them with referent subcohorts totaling 3431 individuals.
• DNA extraction from buccal cell pellets utilized the DSP DNA Virus Pathogen Kit, followed by polymerase chain reaction with 16S ribosomal RNA gene V4 barcoded primers.
• Sequencing was performed using the MiSeq System with 2 × 250-bp paired-end sequencing, and amplicon sequence variants were generated.

TAKEAWAY:

• No overall associations were found between oral microbial characteristics and CRC risk.
• The presence of Olsenella showed a strong positive association with distal colon cancer risk (hazard ratio [HR], 2.16; 95% CI, 1.59-2.95).
• The presence of Prevotella 2 demonstrated a positive association with rectal cancer risk (HR, 1.68; 95% CI, 1.14-2.46).
• Analysis of the unweighted UniFrac principal coordinate analysis vector 2 revealed a strong association with distal colon cancer (HR, 1.29; 95% CI, 1.12-1.49), explaining 6.3% of the variability in the matrix.

IN PRACTICE:

“In this study, there was little evidence for an overall association between the oral microbiome and CRC but we identified associations between specific measures and site-specific CRC risk. Greater alpha diversity was found to be associated with an increased risk of both distal colon and rectal cancer but not proximal colon cancer… Overall, these data support a possible role for oral bacteria in CRC,” wrote the authors of the study.

SOURCE:

The study was led by Emily Vogtmann, PhD, MPH, Division of Cancer Epidemiology and Genetics, National Cancer Institute in Bethesda, Maryland. It was published on March 11 in Cancer.

LIMITATIONS: 

Researchers noted several key limitations, including the collection of oral wash samples from only a single time point for all participants. While oral microbial measures found to be stable over time were likely sufficiently captured, multiple time point sampling would have improved estimation for more variable measures. The questionnaire data was not collected at the time of oral wash collection, with all potential confounders derived from non-contemporaneous baseline questionnaires. Additionally, the timing of oral wash collection, activities before collection, and oral health information were not recorded. The study population consisted primarily of non-Hispanic White individuals of higher socioeconomic status, limiting generalizability. The oral samples were stored for up to 18 years before DNA extraction and sequencing, though the authors note that storage effects should be nondifferential within cohorts.

DISCLOSURES:

This study was supported by the Intramural Research Program of the National Institutes of Health, the National Institute of Environmental Health Sciences (Z01-ES049030), and the National Cancer Institute (Z01-CP010119). The study also received funding from the National Cancer Institute under Contract 75N910D00024 and Grant 1U24CA248454-01. Co-author J. Gregory Caporaso, PhD, disclosed business ownership of Cymis Benefit Corporation. The other authors reported no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.