Two kinds of oral bacteria were associated with an increased risk of pancreatic cancer, according to research presented at the 2016 meeting of the American Association for Cancer Research (AACR), held recently in New Orleans, Louisiana, US.

“A history of periodontal disease and the presence of circulating antibodies to selected oral pathogens have been associated with increased risk of pancreatic cancer in prospective studies; however, relationships of oral microbes with pancreatic cancer have not been directly evaluated,” said Dr. Jiyoung Ahn, associate professor of population health and associate director of population sciences at the Laura and Isaac Perlmutter Cancer Center at NYU Langone Medical Center in New York, New York, US.

“We found that Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, two species of bacteria linked to periodontal disease, were associated with a more than 50 percent increased risk of pancreatic cancer.”

The nested case-control study drew data from two large long-term US-based cancer studies to compare 361 people from whom oral wash samples were collected upon study enrolment and who then developed pancreatic cancer to 371 matched controls. [AACR 2016, abstract 4350]

The researchers genetically profiled all of the bacteria present in the wash samples and analysed the association between the oral microbiota and the risk of pancreatic cancer. They controlled for factors including age, race, sex, smoking status, alcohol consumption, body mass index, a history of diabetes, and the random effects of the cohorts.

P. gingivalis was associated with a 59 percent increased risk of pancreatic cancer (adjusted odds ratio [OR], 1.59; 95 percent confidence interval [CI], 1.15-2.20) while A. actinomycetemcomitans was associated with a 119 percent increased risk (adjusted OR, 2.19; 95 percent CI, 1.15-4.15).

The researchers also found that samples containing more bacteria from the Fusobacteria phylum relative to other types were associated with a decreased risk of pancreatic cancer (OR per percent increase of abundance, 0.92, 95 percent CI, 0.87-0.98).

The risk of developing pancreatic cancer remained even after the researchers excluded patients whose cancer occurred within 2 years of sample collection to avoid counting potential reverse causation.

Oral health, particularly periodontal disease, can contribute to or be affected by cardiovascular disease, diabetes, immune disorders, and cancer, among other conditions.

“Only 5 percent [of people diagnosed with pancreatic cancer] survive 5 years or more after their diagnosis,” Ahn said. “These data do not show a causal relationship, but they are the first steps in understanding a potential new risk factor for pancreatic cancer, which is vital if we are to develop new approaches for pancreatic cancer prevention and early detection in the future.”