The presence of certain bacteria in the mouth may indicate a raised risk for pancreatic cancer - a disease that often begins with no symptoms and for which there is no routine screening test.
The researchers suggest certain bacterial changes in the mouth could potentially show us who is most at risk of developing pancreatic cancer.
This was the main conclusion of a study led by NYU Langone in New York, NY, presented at the American Association for Cancer Research annual meeting in New Orleans, LA, April 16-20, 2016.
The researchers suggest the finding may lead to earlier, more precise treatments for pancreatic cancer, a disease with a pitifully low survival rate as it often escapes early diagnosis.
A history of gum disease and poor oral health have been linked to raised risk of pancreatic cancer, and some studies have also suggested certain types of mouth bacteria may also play a role, but this is the first study to directly evaluate such a link, note the authors.
Senior author Dr. Jiyoung Ahn, epidemiologist and associate professor of population health and environmental medicine at NYU School of Medicine, says:
"Our study offers the first direct evidence that specific changes in the microbial mix in the mouth - the oral microbiome - represent a likely risk factor for pancreatic cancer along with older age, male gender, smoking, African-American race, and a family history of the disease."
Estimates suggest over 46,000 Americans were diagnosed with pancreatic cancer and nearly 40,000 died of the disease in 2014.
Two mouth bacteria linked to raised risk of pancreatic cancer
For their study, the team compared the mouth bacteria sampled from 361 American men and women before they developed pancreatic cancer with those sampled from 371 similar individuals who did not develop the disease.
Fast facts about pancreatic cancer
Pancreatic cancer is the 12th most common cancer in the US
Although rare, the disease is more common in men than in women
Cigarette smoking is the most important risk factor.
The participants were taking part in larger, ongoing studies of cancer risk, where they had been given mouthwash samples when they joined the studies. They were followed for nearly 10 years, during which any cancer diagnoses were noted.
When they analyzed the results, Prof. Ahn and colleagues found that participants whose mouth bacteria contained either of two certain types had a higher risk of developing pancreatic cancer, compared with participants whose oral microbiome showed no evidence of the microorganisms.
Specifically, they found presence of Porphyromonas gingivalis was linked to a 59% overall higher risk of developing pancreatic cancer. Similarly, presence of Aggregatibacter actinomycetemcomitans was linked to a 50% overall higher risk. Both types of bacteria are known to be associated with gum disease or periodontitis.
The figures did not change when the researchers took out cases where participants were diagnosed with pancreatic cancer in the 2 years following collection of the samples. They did this to reduce the chance that the figures were influenced by "reverse causation," that is, the presence of the cancer preceding the presence of the two bacteria.
In another study published recently, the team shows that smoking is tied to dramatic - but not irreversible - changes in mouth bacteria, both in amounts and mix. However, they note that only further studies can show whether changes to mouth bacteria linked to smoking cause pancreatic cancer or affect the immune system.