The Oral Microbiome and Colorectal Cancer: What Does New Research Show?

Colon and rectal cancersare the third most common cancer type worldwide. Although incidence is declining in older age groups, it is steadily increasing in young adults. In recent years, evidence that the gut microbiome may play an important role in colorectal cancer development has grown. However, the role of the oral microbiome was less clear, making it particularly important to investigate the effects of oral bacteria on colorectal cancer.

The Oral Microbiome and Colorectal Cancer

A comprehensive study published on 11 March 2025 in Cancer examined the effects of oral bacteria on colorectal cancer risk. Led by Emily Vogtmann, the research involved three large cohorts: the Agricultural Health Study (AHS), the National Institutes of Health–AARP (NIH-AARP) study and the Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial.

The researchers examined oral samples from a total of 3431 people . DNA extraction and 16S ribosomal RNA sequencing were used to profile the oral microbiome in these samples.

What Do the Findings Show?

The results show that the oral microbiome overall was not clearly associated with colorectal cancer risk when the entire colon and rectum were considered together.

However, when researchers analyzed specific anatomical sites, namely theproximal colon, distal colon and rectum, they found that particular bacteria significantly influenced cancer risk at these sites:

• Olsenella bacteriawere associated specifically with an increase in distal colon cancer risk of 2.16 times .
• Prevotella 2 bacteria were associated with an increase in rectal cancer risk of 68% .

Thus, although an overall assessment appeared to show no association, site-specific analyses identified particular bacteria associated with increased cancer risk at specific locations.

• Oral microbiome diversity (alpha diversity) measured using UniFrac analyses was associated with increased distal colon and rectal cancer risk, but did not affect proximal colon cancer risk.

Meaning and Clinical Significance of the Findings

The authors emphasize that the findings offer a new perspective on understanding site-specific colorectal cancer risks. They provide strong evidence that certain oral bacteria may play an important role in the development of colon and rectal cancers. In the future, this could add new dimensions to diagnostic and risk assessment methods.

Study Limitations

The study has several limitations. Samples were collected only once, and oral hygiene activities and health conditions were not recorded. Participants were also predominantly White individuals with high socioeconomic status, which may limit the generalizability of the findings to the wider population.

Conclusion and Commentary

This study offers important insights into how oral bacteria influence colorectal cancer risk. Future research in different populations, with sampling at multiple time points, could improve understanding of this relationship. Integration into clinical practice could involve regular monitoring of the oral microbiome and its inclusion in colorectal cancer risk assessments.