Cigarettes, H. pylori together greatly multiply risk of gastric cancer

NEW YORK (Reuters Health) - The combination of cigarette smoking and Helicobacter pylori infection, both well-established risk factors for gastric cancer, creates what Japanese researchers say is "a synergistic association" resulting in an 11-fold increase in the risk of gastric cancer.

The researchers' study, headed by Dr. Yutaka Kiyohara of Kyushu University in Fukuoka City, is reported in the Dec. 15 issue of the American Journal of Epidemiology.

The report is the latest from a long-term population-based study in Hisayama, in a populous region on the Japanese island of Kyushu. According to the 1985 census, the age and occupational distributions in Hisayama were almost identical to those in Japan as a whole.

In 1988, 2,752 Hisayama residents aged 40 years or over (more than 80% of the population in that age group) with no history of gastric cancer were screened for the present study. Because the rate of smoking was low among the women, only men, a total of 1,071, were enrolled.

This group was followed for 14 years, until November 2002. The frequency of cigarette smoking was 42.7% and that of H. pylori infection was 76.9%. Participants received health check-ups every 1 to 2 years, and those who moved away were followed by mail or telephone. Comprehensive efforts to identify all cases of gastric cancer in the study cohort included autopsies of 77% of those who died during the study period.

Gastric cancer was diagnosed in 68 participants, including 1 case diagnosed at autopsy. The interval from baseline to time of cancer diagnosis ranged from 0.5 to 13.7 years.

As expected, both cigarette smoking and H. pylori infection were significant risk factors for gastric cancer after adjustment for confounding factors. The researchers estimated the population attributable fraction (PAF) of gastric cancer for cigarette smoking as 28.4% and that for H. pylori infection as 56.2%.

On multivariate analysis, compared with the risk of gastric cancer in non-smokers without H. pylori, hazard ratios for gastric cancer were 5.82 for smokers without H. pylori, 6.93 for non-smokers with H. pylori, and 11.41 for smokers with H. pylori.

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