To date, the extent of the association between H. pylori infection and the incidence of gastric cancer has been unclear.
H. pylori infection and the circulating antibody can be lost with development of cancer. Retrospective studies are therefore subject to bias resulting from classification of cases as H. pylori-negative, when infection has occurred in the past.
However, a new study, carried out by members of the Helicobacter and Cancer Collaborative Group at the University of Leeds, England, has assessed more reliably the relative risk of gastric cancer associated with H. pylori infection.
The research team achieved this by combining data from all case-control studies within prospective cohorts.
A total of 12 studies (10 published, 2 unpublished), encompassing 1228 cases of gastric cancer were included in the evaluation, with individual subject data obtained for each.
Studies were only eligible if blood samples for H. pylori serology were collected before diagnosis of gastric cancer.
Matched odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated for the association between H. pylori and gastric cancer.
This then allowed the variation in relative risk by age, sex, cancer type and subsite, and interval between blood sampling and cancer diagnosis to be investigated.
The study found that the association with H. pylori was restricted to non-cardia cancers (OR 3.0, 95% CI 2.3-3.8).
In addition, this link was stronger when blood samples for H. pylori serology were collected more than 10 years before cancer diagnosis (OR 5.9, 95% CI 3.4-10.3).
|H. pylori infection:
no association with cardia cancers|
However, H. pylori infection was not associated with an altered overall risk of cardia cancer (OR 1.0, 95% CI 0.7-1.4).
Professor D Forman, a member of the research group that conducted the study said that "the results suggest that 5.9 is the best estimate of the relative risk of non-cardia cancer associated with H. pylori infection and that H. pylori does not increase the risk of cardia cancer."
He added, "The results also support the idea that when H. pylori status is assessed close to cancer diagnosis, the magnitude of the non-cardia association may be underestimated."