People with H. pylori who were treated had about a 63% lower risk of developing noncardia gastric adenocarcinoma (NCGA) after 8 years of follow-up, compared with peers with H. pylori who were not treated.
The U.S. data align with previous studies, conducted mostly in Asia, that found that treating the infection can reduce stomach cancer incidence.
The KPNC study shows the “potential for stomach cancer prevention in U.S. populations through H. pylori screening and treatment,” study investigator Dan Li, MD, gastroenterologist with the Kaiser Permanente Medical Group and Kaiser Permanente Division of Research in Oakland, Calif., said in an interview.
Judith Kim, MD, a gastroenterologist at NYU Langone Health in New York, who wasn’t involved in the research, said that the study is significant because “it is the first to show this effect in a large, diverse population in the U.S., where gastric cancer incidence is lower.”
The study was published online in Gastroenterology.
Top risk factor
About 30% of people in the United States are infected with H. pylori, which is the No. 1 known risk factor for stomach cancer, Dr. Li said.
The study cohort included 716,567 KPNC members who underwent H. pylori testing and/or treatment between 1997 and 2015.
Among H. pylori–infected individuals (based on positive nonserology test results), the subdistribution hazard ratio was 6.07 for untreated individuals and 2.68 for treated individuals, compared with H. pylori–negative individuals.
It’s not surprising that people who were treated for the infection still had a higher risk of NCGA than people who had never had the infection, Dr. Li said.
“This is likely because many people with chronic H. pylori infection had already developed some precancerous changes in their stomach before they were treated. This finding suggests that H. pylori ideally should be treated before precancerous changes develop,” he said.
When compared directly with H. pylori–positive/untreated individuals, the risk for NCGA in H. pylori–positive/treated individuals was somewhat lower at less than 8 years follow-up (sHR, 0.95) and significantly lower at 8+ years of follow-up (sHR, 0.37).
“After 7-10 years of follow-up, people with H. pylori who received treatment had nearly half the risk of developing stomach cancer as the general population,” Dr. Li said. “This is likely because most people infected with H. pylori in the general population are not screened nor treated. This highlights the impact screening and treatment can have.”
The data also show that cumulative incidence curves for H. pylori–positive/untreated and H. pylori–positive/treated largely overlapped during the first 7 years of follow-up and started to separate after 8 years.
At 10 years, cumulative NCGA incidence rates for H. pylori–positive/untreated, H. pylori–positive/treated, and H. pylori negative were 31.0, 19.7, and 3.5 per 10,000 persons, respectively (P < .0001).
This study shows that treating H. pylori reduces stomach cancer incidence in the United States, thus “filling an important research and knowledge gap,” Dr. Li said.
In the United States, Asian, Black, and Hispanic adults are much more likely to be infected with H. pylori, and they have a two- to threefold higher risk of developing stomach cancer, he noted.
“This suggests it may be reasonable to consider targeted screening and treatment in these high-risk groups. However, the optimal strategy for population-based H. pylori screening has not been established, and more research is needed to determine who should be screened for H. pylori and at what age screening should begin,” Dr. Li said.