Estimating cancer risks to a population.

Three important issues impinge on estimating the risk of cancer to a population: (1) How can one use epidemiologic studies on one population to tell us what is likely to happen to other populations? (2) How can one use nonhuman data (i.e., laboratory experiments) to tell us what is likely to happen to humans? (3) What reasonable assumptions can be used to guide the logical extension of information from the laboratory to expectations for man, and what research is needed to support or modify these assumptions? Four principles currently guide our laboratory-to-man extrapolations: effects in animals, properly qualified, are applicable to man; methods do not now exist to establish a threshold for long-delayed effects such as cancer; the exposure of experimental animals to high doses is a necessary and valid method of discovering possible carcinogenic hazards in man; materials should be assessed in terms of human risk rather than as "safe" or "unsafe".