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

Abstract

The highest incidence of stomach cancer worldwide and a relatively high incidence of liver cancer are found in the Japanese population. 1 There is considerable geographical variation in cancer mortality in Japan: e.g. the western region has a higher liver cancer mortality rate than the northern region. 2 Such differences in mortality might be explained by hepatitis virus infection in the case of liver cancer, [3][4][5][6][7][8] and by diet and Helicobacter pylori infection in the case of stomach cancer. 9 However, statistics indicate that other environmental factors play an important role in carcinogenesis for such sites. For example, an increasing trend of liver cancer mortality is observed in men but not in women, 10 despite the absence of a gender difference in hepatitis viral infection rates. 11 Liver and stomach cancers are not generally considered to be causally related to cigarette smoking. 12 Although an elevated risk of these cancers in smokers has been observed in a number of studies, including large-scale cohort studies, [13][14][15][16][17][18] the magnitude of the association was relatively small. 19 In fact, contradictory findings were shown for these cancers in previous studies, including those on Japanese subjects. 4,13,16,[20][21][22][23][24][25][26][27] The present study examined prospectively, using data from a study that was conducted in the region with the highest mortality rate for liver cancer in Japan, whether cigarette smoking increases the risk of liver and stomach cancers. © International Epidemiological Association 2000 Printed in Great BritainProspective 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 the liver and stomach. The authors examined prospectively the relationship between smoking and these cancers in an endemic region. MethodsThe data used were a cohort study on the relationship between lifestyle and health in the region having the highest liver cancer mortality in Japan. Of the cohort members, 4050 males aged у40 years were included in the present analysis with a 9-year mean follow-up. Cox proportional hazards regression was used to estimate relative risks (RR) for cancer of the liver, stomach, smokingrelated sites and others, while adjusting for age, residence, and alcohol intake. ResultsBy the end of the study period, 59 cases of liver cancer and 53 cases 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 had almost the same risk of these cancers as heavy smokers, while they showed a relatively low risk of smokerelated cancers. ConclusionsThe present results indicate that smoking is a risk factor of liver and stomach cancer in a ...

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