[20 years of cancer epidemiology. The epidemiologist's viewpoint]

It is indeed a challenge to summarize in a few pages, 20 years of research in cancer epidemiology and the answer can only be very limited. Our understanding of risk factors has progressed both by a better evaluation of the importance of known factors and by the identification of new factors, in particular infectious and hormonal factors. Direct assessment of primary prevention activities has proved to be very difficult because more than 30 years may be required between a reduction in exposure to a carcinogenic substance and the observation of its consequences in terms of public health. The epidemiological knowledge of health care workers, media, decision markers and the general public has improved and all now know the main risk factors for cancer. However, the relative importance of these factors is poorly measured and unfounded fears about substances which are almost certainly not carcinogenic, are adding to the confusion.