[Screening from the epidemiological viewpoint].

The scope of screening is to identify disease in a clinically inapparent stage in order to treat more effectively. However, the required application of a test to large subsets of the population implies risks which cannot be ignored. Thus, the introduction of a test for use in screening without previously established evidence of a benefit which exceeds potential harm by far cannot be justified. With regard to cancer, evidence of effectiveness has been proven for screening on cervical (Papsmear), breast (mammography) and colorectal (faecal occult blood test) cancer. The routine application of a screening procedure which has been proven effective provides the benefit in terms of mortality reduction seen in the trials only if the entire screening chain, from the test over potentially required assessment to treatment, is offered with highest quality and is under permanent quality control.