[Methods and intervention in populations with high-risk for cancer].

Prevention envisions either a reduction in the incidence of a disease through direct action against its causes, or a reduction of the consequences of that disease (especially mortality), by action against the process leading to clinical expression of the underlying pathology. As in therapeutic medicine, preventive measures must be thoroughly evaluated for efficacy and secondary effects before they become standard recommendations. Two levels of evaluation can be identified: evaluation of feasibility, acceptability, involving quality control of the proposed programme, evaluation of results according to previously defined and quantified objectives. In order to demonstrate that the risk-benefit ratio of a preventive strategy is favorable, results in the intervention group must be compared with those in the control group, just as is done in therapeutic trials. Further more, prevention applies generally to healthy subject ie those not needing medical care and for whom, in the majority of cases, there will be no direct benefit. As a consequence, careful ethical consideration must be given to such programme. In particular, calculating the risk-benefit ratio must take into account the mental and social well being of people whose lives will be "medicalized" as a result of such intervention. Measurement of the consequences of such preventive actions on the life style and mental health of the population subjected to them necessitates the development of specific tools adapted to such situations. Research in methodology in this area is essential. If a population with almost 100% risk for a disease can be identified (genetic risk for example), aggressive preventive intervention can be limited to only that group. It must be emphasized that identification of subjects at risk, no matter how reliable, is not an end in itself. It is only justified, on a medical point of view, if we can offer these individuals a preventive programme with demonstrated benefit. The primacy of collective benefit over individual interest mandates that preventive intervention be based on voluntary informed consent of the target population. An alternative to individual consent could be, in some occasion, a "collective" consent.