A large-scale cohort study on risk factors for primary liver cancer, with special reference to the role of cigarette smoking.

A large-scale cohort study in Japan (1966-1982) of life styles and primary liver cancer in men (123 out of 1,709,273 person-years) revealed a close association with cigarette smoking comparable to that for lung cancer, the relative risk (r.r.) for those smoking 1-29 and 30 or more cigarettes daily being 3.09 (1.78-5.35), 6.83 (3.56-13.10) for liver cancer, and 4.45 (3.77-5.25), 6.80 (5.51-8.41) for lung cancer, respectively. For liver cirrhosis, daily cigarette smoking was of less importance compared to daily alcohol drinking, r.r. = 1.17 (1.00-1.36) and 1.82 (1.63-2.04). However, for liver cancer, the risk from daily cigarette smoking was much higher than from daily alcohol drinking, r.r. = 3.14 (1.82-5.42) and 1.89 (1.40-2.55). The risk of liver cancer among the liver cirrhosis cases was therefore calculated as 2.67 (1.49-4.79) for daily cigarette smokers and 1.00 (0.72-1.38) for daily alcohol drinkers. These results must be of special importance in interpreting the reason for the increasing, unique mortality trend of liver cancer in men in recent years in Japan.