Biological Aspects of Associations between Environmental Exposures and Cancer

The complexity of human cancer biology makes attribution of cause an uncertain exercise.Causes of human cancer act together to produce some 200 different conditions called cancers.While several exposures are important in human cancer, for example, smoking and general dietary factors, examples of inherited susceptibility to cancer illustrate how host factors might be equally important.Discussions of causes of human cancer must take note of the uncertainties in our knowledge of genetic susceptibility, mechanisms of action of known cancer causing exposures, and identification of all important causes.These uncertainties should not detract, however, from efforts to deal with the major and well understood cause of one-third of U.S. cancer deaths: cigarette smoking.