The epidemiology of cancer: an overview.

The contribution of cancer epidemiology to cancer prevention is in identifying risk factors, providing clues for understanding etiologic mechanisms, and in developing the scientific rationale for the effective application of preventive measures. Cancer mortality, incidence, and survival trends over 25 years (1950-1974) in the United States are reviewed for 12 selected sites in adult men and women. If both incidence and mortality for a specific cancer site remain unchanged or change proportionately over a period of years, no major change in survival should be anticipated. The patterns of occurrence and their etiologic implications are reviewed separately in American blacks and in children and young adults. The studies of geographic pathology and of various migrant populations have provided observational "experiments of nature" that have facilitated our understanding of cancer etiology by stimulating important paths of research.