Tumor enhancers: underestimated factors in the epidemiology of lifestyle-associated cancers.

Model studies in carcinogenesis give ample evidence of synergistic, tumor-promoting and cocarcinogenic effects of environmental agents and dietary factors in regard to the induction and propagation of neoplasms. This presentation examines tumor enhancers deriving from the use of tobacco and alcohol as well as the effects of dietary fat and other food components on endocrinological and gastrointestinal factors that contribute to tumor development in the breast and colon. It is suggested that epidemiologic surveys need to intensify investigations on the interrelationship of tumor enhancers and genotoxic agents in high risk populations and that they need to study especially the dose-response effects of such agents. Experimental studies should focus increasingly on epidemiologic leads that suggest potential enhancers of genotoxic agents and should delineate mechanisms involved in such multistep carcinogenesis processes. This approach would be a prerequisite for chemoprevention. Recommendations for changes of lifestyle habits and practical approaches towards reduction of tumor enhancers in consumer goods and in the environment are additional requirements for appropriate preventive strategies.