[Markers of exposure and early lesions in cancer epidemiology]

The biological markers of risk can be separated into two categories: markers of exposure to a specific substance, based on several biochemical, physical and immunological methods (usually able to measure the absorbed dose); markers of early lesions which usually are not specific for a particular substance and do not estimate the dose of exposure. In epidemiological research on cancer etiology, biological markers have a different role according to whether cases are subjects with early lesions or with invasive cancers. The first approach has the advantage of shortening the observation time between exposure and the appearance of a biological effect. On the other hand, the biological relevance of the study could be limited due to the non univocal relation between early lesions and cancer. With the second approach, invasive cancer can be related to specific markers of exposure (this would permit to draw direct inference on disease etiology) or to markers of early lesions (etiological interpretation in this case would be less straightforward). The two approaches should be considered in the frame of two basic problems: What is the advantage of measuring exposure at the individual level? What is the advantage of a biological marker as compared to traditional epidemiological methods? With studies at the group level the correlation between exposure variables and disease frequency can be estimated. Nevertheless only studies at the individual level can exclude the fact that the observed correlation is due to an artefact. In this case we are left with the second question and many answers are possible.(ABSTRACT TRUNCATED AT 250 WORDS)