Colorectal cancer: what does our oral microbiota reveal?

A group of Irish researchers has shown that bacteria of the oral cavity might play a role in the development of gastrointestinal cancer. Their detection in the intestines could help identify early on individuals at risk.


Several studies have previously shown that the intestinal microbiota of colorectal cancer patients is disrupted. Some have also suggested that certain bacteria might encourage the onset of this disease. Some of the carcinogenic bacteria in question are thought to come from our oral cavity. In the scientific journal Gut, researchers from the National University of Ireland show that several bacterial species naturally present in our mouths travel down the digestive tract; once in the colon, they are thought to play a role in the development of cancer.

Protective species?

To reach this conclusion, the scientists analyzed samples of saliva, colonic mucosa and stools obtained from 99 patients suffering from colorectal cancer, 32 patients presenting with intestinal polyps (benign tumors liable to develop into malignant tumors) and 103 healthy volunteers. Firstly, the analysis indicated that colonization of the intestines by bacteria from the oral cavity was increased in patients suffering from cancer or polyps compared to healthy subjects. The results also showed that certain bacteria seem to prevent the implantation of pathogenic bacteria associated with colorectal cancer. The authors consider that their beneficial presence would be promoted by a balanced diet, low in fat and sugars.

Early detection of individuals at risk

The study also revealed that the intestines of these three groups did not harbor the same bacterial populations. The researchers suggest that it these populations could be used to distinguish between cancer patients, individuals with polyps and healthy subjects. And, by looking for specific bacteria in the saliva, they correctly identified more than one in two cancer patients, and two out of three patients with polyps. In combination with a stool analysis, the results are even more accurate: three-quarters of cancer cases and almost 90% of patients with polyps were correctly detected. The researchers however concede that larger scale studies, which will take the age of volunteers into account, as well as their consumption of tobacco and alcohol and disease stage, are essential to confirm these promising results.



Flemer B, Warren RD, Barrett MP, et al. The oral microbiota in colorectal cancer is distinctive and predictive. Gut 2018;67:1454-1463