Researchers at NYU Langone’s Perlmutter Cancer Center reported that at least three kinds of oral bacteria in Americans might heighten or lower their risk of developing esophageal cancer—the sixth most common cause of cancer-related death worldwide.

Published online in Cancer Research in December 2017, an analysis of data from two national cohorts involving more than 120,000 patients found a 21 percent increased cancer risk tied to the presence of Tannerella forsythia, a bacterium commonly linked to gum disease. By contrast, types of Streptococcus and Neisseria bacteria were associated with as much as a 24 percent decrease in risk for esophageal cancer. Neisseria are known to break down the toxins in tobacco smoke, and smokers are known to have lower amounts of these bacteria in their mouths than nonsmokers.

The oral microbiome—which can be changed by smoking, heavy drinking, diet, gum disease, or gastric reflux—has long been thought to influence risk of esophageal adenocarcinoma or squamous cell carcinoma, say the researchers. But they add that the new study, which monitored healthy patients for as long as 10 years, is the first to identify which among nearly 300 kinds of bacteria commonly found in the mouth are statistically linked to the risk of getting either of the 2 most common forms of esophageal cancer.

“Our study brings us much closer to identifying the underlying causes of these cancers, because we now know that at least in some cases disease appears consistently linked to the presence of specific bacteria in the upper digestive tract,” says study senior investigator and epidemiologist Jiyoung Ahn, PhD, associate professor of population health and medicine and associate director for Population Research at Perlmutter Cancer Center. “Conversely, we have more evidence that the absence or loss of other bacteria in the mouth may lead to these cancers, or to gut diseases that trigger these cancers.”

That said, the researchers emphasized that their findings do not demonstrate that the bacteria directly cause or prevent esophageal cancer. Postdoctoral fellow and study lead investigator Brandilyn Peters, PhD, says the team next plans to analyze the main biological functions of some bacteria in the mouth to see how these metabolic pathways may influence cancer risk.