Do bacteria cause stomach cancer?

“Stomach cancer is the fourth most commonly occurring cancer in men and the seventh most commonly occurring cancer in women,” explain the World Cancer Research Fund and the American Institute for Cancer Research.

The highest stomach cancer rates in 2018 were seen in South Korea, Mongolia, Japan, and China.

The National Cancer Institute (NCI) note that in the United States, there were 97,915 people diagnosed with stomach cancer in 2015.

One risk factor for stomach cancer is infection with a type of bacteria called Heliobacter pylori, but the specifics of its impact on the development of tumors has been unclear.

Now, however, a team of researchers at the Fred Hutchinson Cancer Research Center in Seattle, WA, have pinpointed which specific H. pylori strain may be responsible for increased stomach cancer risk.

The researchers’ findings, which they report in a study paper published in the journal PLOS ONE, may change the way in which specialists screen for and treat this type of cancer.

Harmful bacterial strain identified

Senior researcher Dr. Nina Salama and team — in collaboration with researchers from Zhengzhou University in China — collected and analyzed samples from stool and from stomach endoscopies from 49 participants.

The scientists were aiming to see which kinds of H. pylori would be associated with stomach cancer.

Through their analysis, they identified one strain that stood out from the rest: H. pylori with a variant of the cytoxin-associated gene A — namely, the EPIYA D variant. Of the study participants with this strain, 91 percent had a diagnosis of stomach cancer.

“We’ve known the H. pylori bacterium has a strong correlation to stomach cancer, but it’s been difficult to pinpoint why certain patients, especially in areas like Northeast Asia, are more susceptible to stomach cancer,” notes Dr. Salama.

“While [the recent study is] preliminary in nature, these results could be the first step towards identifying the highest-risk groups and improving screening and treatment plans,” she adds.

‘A clear target to develop vaccines’

This information, Dr. Salama believes, could provide specialists with a new therapeutic target, thereby allowing them to develop better defenses against stomach cancer.

“Unfortunately, infections like H. pylori directly or indirectly, cause up to 20 percent of cancers worldwide. But knowing the cause gives us a clear target to develop vaccines for prevention or tools to better recognize risk.”

Dr. Nina Salama

At the same time, however, the researchers admit that their study was small and had a limited number of participants. This means that they cannot yet extend their findings to the general population.

In the future, the scientists would like to conduct more studies investigating the mechanisms through which H. pylori may impact cancer risk.

“Further studies,” the authors conclude, “will need to be done to investigate the factors that contribute to the observed higher H. pylori load in the stool among gastric cancer subjects compared to noncancer subjects despite a similar H. pylori load in the stomach.”

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