ABSTRACT
Cancer is a collection of about 200 diseases grouped together because of their similar growth processes. Each cancer, regardless of the part of the body it affects, is believed to originate from a single "transformed" cell. Relating exposures and behaviors to cancer occurrence is a first step in cancer prevention. Nationwide mortality data are used to answer questions about the number of deaths caused by cancer in the United States. Cancer causation is thought to involve at least two steps: an early initiation step and a later promotion effect. Synergism, a form of interaction, occurs when two or more substances potentiate each other's effects, producing more cancers than can be accounted for by adding the effects of each. The Federal Government has centered efforts to control cancer on reducing exposures to chemical and physical carcinogens. Carcinogens can be identified through epidemiology—the study of diseases and their determinants in human populations—and through various laboratory tests.
