H. pylori live in the human stomach. But many people with H. pylori infections never develop gastric cancer. Some evidence suggests that genetic variation among different strains of the bacteria may explain why some infections result in gastric cancer while others do not.

Martyn Plummer of the International Agency for Research on Cancer in Lyon, France, and colleagues examined the relationship between several strains of H. pylori and the development of gastric cancer. They analyzed gastric biopsy specimens from 2,145 participants in a chemoprevention trial in Venezuela.

The researchers found a strong association between precancerous gastric lesions and infection with particular strains of H. pylori. “Our study adds to the emerging body of evidence that the strength of the association between H. pylori and gastric [cancer] has been underestimated. In a recent review of infection-related cancer, the proportion of all gastric cancers worldwide attributed to H. pylori was estimated to be 63%. Our results imply that, in populations with a high prevalence of [disease-causing] H. pylori, the attributable fraction may be even higher,” the authors write. -Journal of the National Cancer Institute