FROM THE AACR ANNUAL MEETING
Two species of oral bacteria – Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans – have been linked with an elevated risk of developing pancreatic cancer. This follows previous studies linking poor oral health in general to an increased risk of pancreatic cancer.
“Each [species] is associated with more than 50% higher likelihood to develop pancreatic cancer,” Jiyoung Ahn, Ph.D., of New York University Langone Medical Center, said during a news conference at the annual meeting of the American Association for Cancer Research.
“The findings suggest that carriage of these bacteria is related to subsequent development of pancreatic cancer,” said Dr. Ahn. Given the poor survival rate for pancreatic cancer of 5% at 5 years, identifying risk factors for its development may have implications for screening tools and prevention if the associations are found to be causal.
Employing a prospective, nested case-control study design, Dr. Ahn used samples and data from the Cancer Prevention Study II and the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial cohorts. Both of those studies enrolled healthy people and followed them for several years looking for a variety of outcomes, including cancer. Researchers performed genomic analysis on oral wash samples collected at the beginning of the studies to identify the bacterial species present. Samples from 361 people who eventually developed pancreatic cancer were matched to 371 controls.
After adjustment for covariates of age, race, sex, smoking status, alcohol consumption, body mass index, and diabetes, logistic regression analysis showed that the presence of P. gingivalis in the samples was associated with a 59% increased risk (adjusted odds ratio [OR] = 1.59; 95% confidence interval [CI] 1.15, 2.20) of developing pancreatic cancer, and the presence of A. actinomycetemcomitans was associated with a 119% increased risk (OR = 2.19; 95% CI 1.15, 4.15). The presence of these bacteria remained a risk factor even after the deletion of samples from people who developed pancreatic cancer within the 2 years after collection of their samples to eliminate the possibility that early pancreatic cancers were affecting the populations of bacteria present.
Greater relative abundance of Fusobacteria species was associated with a lower risk (OR per percent increased abundance = 0.92; 95% CI 0.87, 0.98).
“Why this is important is because this is the first evidence suggesting the oral bacteria and pancreatic cancer relationship,” Dr. Ahn said, adding that she foresees eventual clinical applications. “In the long run, knowing these bacteria, we can see who’s more likely to develop pancreatic cancer, and in the more long run, we see that maybe we can control these bacteria … to prevent pancreatic cancer.”
So far, she said no mechanisms are known to account for the association between bacteria and pancreatic cancer risk although several have been proposed. She said a next step is to collect pancreatic tissue to see if oral bacteria are traveling to the pancreas.
Dr. Ahn noted that a major limitation of the study was that the populations involved in the cohorts from which the oral wash samples were obtained were mainly non-Hispanic whites, so the findings may not be generalizable to other groups.
Dr. Ahn had no disclosures.