[Evidence of effectiveness and prevention of occupational cancer].

The persistence of exposure to carcinogens at work in member States of the European union and in other industrialised countries has been repeatedly reported, and prompts for the epidemiologic assessment of trends in cancer risk according to changes in exposure distribution. Epidemiological evidence of risk reduction could be produced for all agents classified by the International agency for cancer research as Group 1 agents (human carcinogens). However, such evidence is available only for a much more limited number of agents. Benzene and asbestos are used as case-studies, given the very large number of epidemiological studies conducted on populations exposed to them. Only five studies assessed cancer risk after exposure cessation, and in four of them cessation was due to dismission of the industrial activities rather than to the introduction of industrial hygiene measures. The bases for assessment of effectiveness in the field of occupational (and environmental) prevention differ from those of evidence-based medicine. The burden of proof should be on the employer to demonstrate that a given industry can be operated safely; once evidences of adverse effects have been found, that should be per se sufficient to enforce strict control of exposures. From a methodological point of view, it would be either impossible or unethical to conduct controlled trials to assess effectiveness, and in general the highest level of evidence that can be reasonably achieved is that provided by observational studies.