Report by the Research Committee of the Ministry of Education, Science, Sports and Culture on evaluation of risk factors for cancer.

Lifestyle habits and other living conditions in Japanese have progressively been changing after the World War II, and the changing trend has been accelerated since 1970. The frequency and distribution of cancer by site in Japan showed marked secular changes during the past decades, just as reflecting the above changes in environmental factors. A large scaled cohort study on cancer at moment was strongly anticipated in Japan, after the cohort study by Dr. Hirayama et al. had ended around 1980 with unexpectedly fruitful results. However, financial problems and other conditions hindered to start such cohort studies. A multicentered collaborative cohort study had planned among the epidemiologists and epidemiology oriented clinicians who have been working on cancer in the communities, resolving problems on cost and others for long term epidemiological issues. A new cohort with a total of 125 thousands of healthy inhabitants living in the areas scattered throughout country was established in 1988-1990, although they were not randomly distributed in area. Some 30 thousands industrial worker cohort has joined in this study, which will be separately analysed. The study was partly granted by the Ministry of Education, Science, Sports and Culture and largely supported by local government and volunteers in each area for ten years. A research committee on this study was organized and are following up all subjects participated for more than ten years, mainly pursuing mortality status, and incidence of cancer for about half population of the cohort is also under study. About 1,000 deaths per year were observed in the first four years and more than 30% were due to cancer. The proportion of moved out of town was small being about 1% per year. The distribution of cancer deaths by site for the first four years was similar to those of general population. This report summarized the study plan and the epidemiological characteristics of the cohort at entry of the study. It also gives a brief account of activities until 1994.