oral microbiota and pancreatic cancer

A large case-controlled study shows the association between human oral microbiota and pancreatic cancer risk.

Pancreatic cancer is the 12th most commonly occurring cancer worldwide and the 7th leading cause of cancer-related death. Due to its high lethality, the five-year survival rate is estimated to be 24% at early diagnosis and 1.8% by advanced-stage diagnosis. Prevention strategies for pancreatic cancer are imperative, however, the etiology of this disease is poorly understood. Cigarette smoking is one of the few established risk factors that has been linked to cancer development. Other modifiable exposures include obesity, diabetes, and chronic pancreatitis that are often seen in pancreatic cancer patients. Of interest, recent research has associated periodontal disease, also known as gum disease, with increased pancreatic cancer risk.

Oral health and disease are closely tied to changes in oral microbial status. The oral microbiome consists of over 700 species of bacteria that colonize the human mouth. Distinct oral microbial ecosystems have been characterized for conditions like gingivitis and dental caries. Specific microbes, including Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, have been implicated in periodontal disease etiology. This evidence suggests that changes in oral microbiota may mediate the relationship between periodontal disease and pancreatic cancer risk. To date, few robust epidemiological studies have been conducted examining the relationship between oral microbes and pancreatic cancer.

Researchers from the National Cancer Institute and Tehran University of Medical Sciences compared the oral microbiota of patients with pancreatic cancer (cases) to non-cancerous controls. Briefly, 273 cases and 285 clinic-based controls were enrolled from hospitals and clinics in Tehran, Iran from 2011 to 2015. DNA was extracted from patient saliva samples to determine the individual’s oral microbial profile.

The researchers found that the overall oral microbial communities in pancreatic cancer cases were significantly different from that of controls. Moreover, specific microbial taxa were associated with the presence of pancreatic cancer. Increased levels of Haemophilus was associated with reduced odds of pancreatic cancer, while the presence of Enterobacteriaceae, Lachnospiraceae, Bacteroidaceae, and Staphylococcaceae was associated with greater odds of pancreatic cancer. In this study, the periodontal pathogen, P gingivalis was not associated with increased risk of pancreatic cancer, while the presence of A. actinomycetemcomitans did confer additional risk. The findings were published in Cancer Medicine.

The authors acknowledged several limitations inherent to the case-control study design. Since saliva samples were collected at the time of diagnosis, it is difficult to show a causal relationship between microbial composition and pancreatic cancer risk. It is unknown if the differences in oral microbiota were present before the development of pancreatic cancer or post-onset of the disease. Additionally, the control group consisted of hospital- and clinic-based patients who did not have pancreatic cancer, but may have been referred for other underlying conditions that affected their microbial status.

Large, prospective cohort studies are required to further validate these findings. Ultimately, the identification of oral microbiota related to cancer development may provide predictive biomarkers for the early detection of pancreatic cancer.

Written by Cheryl Xia, HBMSc

References: Vogtmann, E. et al. Oral microbial community composition is associated with pancreatic cancer: A case‐control study in Iran. Cancer Med cam4.2660 (2019) doi:10.1002/cam4.2660.

Image by Arek Socha from Pixabay

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