Prospective study on the relation of cigarette smoking with cancer of the liver and stomach in an endemic region

Background Smoking has not been confirmed as a risk factor for cancers of t he liver and stomach. The authors examined prospectively the relationship b etween smoking and these cancers in an endemic region. Methods The data used were a cohort study on the relationship between lifes tyle and health in the region having the highest liver cancer mortality in Japan. Of the cohort members, 4050 males aged greater than or equal to 40 y ears were included in the present analysis with a 9-year mean follow-up. Co x proportional hazards regression was used to estimate relative risks (RR) for cancer of the liver, stomach, smoking-related sites and others, while a djusting for age, residence, and alcohol intake. Results By the end of the study period, 59 cases of liver cancer and 53 cas es of stomach cancer were identified. Current smokers, compared to subjects who had never smoked, had a threefold risk of liver cancer (RR = 3.3; 95% CI: 1.2-9.5) and a twofold risk of stomach cancer (RR = 2.2: 95% CI: 0.8-5. 7). Sub-cohort analysis showed that adjustment for history of chronic liver disease did not attenuate the risk of liver cancer. Light/medium smokers h ad almost the same risk of these cancers as heavy smokers, while they showe d a relatively low risk of smoke-related cancers. Conclusions The present results indicate that smoking is a risk factor of l iver and stomach cancer in a population with a high background risk for the se cancers. However, causal inferences should be made cautiously due to a l ack of information on known risk factors.