Epidemiological discovery of occupational cancers.

Most occupational hazards of cancer that have been recognized have been discovered as a result of clinical intuition or epidemiological observation. Most could, however, have been avoided if modern laboratory techniques had been used to test the substances used before men and women were deliberately exposed to them. Industry must be expected to use such tests in the future and it is hoped that few occupational hazards of cancer will be introduced. Laboratory studies, however, are not 100% reliable as predictors of human risk and epidemiological observations will continue to be required to: detect existing hazards that have been overlooked, pick up new hazards that were not predicted by laboratory investigation, determine the level of risk that is socially acceptable, if a carcinogenic agent has to be used, and sometimes to demonstrate the safety of an agent that has been suspected of causing a hazard to man on uncertain grounds. The ways in which epidemiological observations can be used for these purposes are discussed.