The study — led by NYU Langone Health's Perlmutter Cancer Center in New York, NY — also reveals that some types of mouth bacteria are linked to lower risk of esophageal cancer.

Reporting in the journal Cancer Research, the researchers note that they ruled out potential effects from smoking, alcohol, and body mass index (BMI) when they analyzed the data.

Senior investigator of the study Jiyoung Ahn, an associate professor and epidemiologist at NYU School of Medicine, believes that the findings will take us closer to establishing the causes of esophageal cancer.

She says that this is "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."

'Urgent need' for new prevention strategies

Esophageal cancer is a cancer that starts in the cells of the esophagus, the tube of muscular tissue that moves food from the mouth to the stomach, and which is commonly referred to as the food pipe, or gullet.

The disease accounts for around 1 percent of all diagnosed cancers in the United States, where every year about 16,940 people find out that they have the disease and 15,690 die of it. The cancer is more common in men than in women.

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Because the lining of the esophagus has two main types of cell, there are two main types of esophageal cancer: esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC). The new study investigated both EAC and ESCC.

Unfortunately, because most people do not discover that they have esophageal cancer until the disease is advanced, only between 15–25 percent of them survive more than 5 years.

"Esophageal cancer is a highly fatal cancer," says Prof. Ahn, "and there is an urgent need for new avenues of prevention, risk stratification, and early detection."

Oral microbiota and links to cancer

The human mouth is home to hundreds of species of bacteria and other single-celled organisms. These "oral microbiota" occupy various habitats in the mouth, such as the gums, teeth, tonsils, tongue, cheeks, and palates.

Studies have shown that the composition of oral microbiota changes with different habits — such as heavy alcohol use, smoking, and diet — and also in response to disease, such as gum (or periodontal) disease and gastric reflux.

There is also evidence that some types of oral microbiota that cause gum disease are linked with cancer of the head and neck.

Prof. Ahn and colleagues note that — mainly as a result of studies that use data from one point in time — there is a long-held view that the composition of oral microbiota influences the risk of developing EAC and ESCC.

But the new study, which followed healthy patients for a decade, is the first to identify, from the hundreds of different types, which specific mouth bacteria are linked to risk of EAC and ESCC.

Some bacteria raise esophageal cancer risk

For their analysis, the team analyzed the microbiota in oral wash samples taken from more 122,000 people who took part in two national studies. The participants were followed for 10 years, during which researchers noted who developed esophageal cancer.

The team compared the genetic information of the mouth microbiota — the "oral microbiomes" — of the participants who developed esophageal cancer with that of equivalent participants who did not develop the disease.

They found that the presence of Tannerella forsythia was tied to higher risk of EAC, and that "abundance" of Porphyromonas gingivalis was tied to higher risk of ESCC.

In contrast, they also identified two types of bacteria — Streptococcus and Neisseria — that were linked to a lower risk of esophageal cancer.

The second of these, Neisseria, is known to play a role in the breakdown of toxic substances in tobacco smoke and is found in greater abundance in the oral cavities of nonsmokers than smokers.

"Our study indicates that learning more about the role of oral microbiota may potentially lead to strategies to prevent esophageal cancer, or at least to identify it at earlier stages."