The epidemiology of cancer.

The epidemiology of cancer has a long history. It led to the discovery of several causes of cancer before techniques for the production of the disease in laboratory animals became available. In recent years, epidemiological studies have contributed to knowledge of cancer in five ways: by demonstrating geographical and temporal variations in incidence, by correlating incidence in different communities with the prevalence of social habits and environmental agents, by comparing the experience of individuals with and without cancer, by intervening to remove suspected agents and observing the results, and by making quantitative observations that test the applicability to man of models of the mechanism by which the disease is produced. Joint investigation of dietetic factors by epidemiologists and laboratory workers offers the brightest prospect of discovering new ways of preventing cancer in the near future. Advances in knowledge will eventually prevent the need for learning about cancer by seeing its production in man, but epidemiological enquiry will be needed for many years to monitor preventive programs and to provide quantitative measures of risk from hazards that cannot be avoided completely.