[Precursor lesions: epidemiology--is there enough evidence?].

Exact knowledge of the incidence and prevalence of precursor lesions of malignant diseases would be of great value for the precise evaluation of their potential clinical-pathological progression and therefore for planning and intervention in individual cases and also for planning and evaluation of prevention and early detection strategies. Concerning these high expectations it is surprising that precise data on incidence, prevalence and the exact risk for progression are lacking. Sources of data (cancer registries, specific registries for precursor lesions, early detection programs and specific designed studies) are analyzed concerning their validity and reliability. Imprecise and redundant terminology represents a crucial reason for the lack of data availability.