[Methodological framework of the evaluation of systematic screening and treatment of preexistent lesions of the colon and the rectum].

Among the conditions which need to be filled when generalizing the mass screening of polyps in view of the secondary prevention of colorectal cancers, three are already present: 1) it is a frequent and serious cancer; 2) there is an affiliation between benign tumours and cancer; 3) an effective non-mutilating treatment of benign tumours is available. On the other hand, two additional conditions remain unfilled and yet lie within the domain of research by methodologically rigorous studies: the setting up of a screening test with a high cost-effectiveness relationship; the epidemiological demonstration of the decreasing incidence of colorectal cancers following screening and treatment of precancerous lesions.