[Colorectal cancer. Precancerous conditions].

Colorectal precancerous stages are primarily benign lesions of the colon mucosa with a potential to malignant degeneration. They are macroscopically seen as polypoid lesions, but not only "adenomas" are to be seen as precancerous. Polypoid lesions which are not of neoplastic origin are not capable of malignant degeneration. Precancerous dysplasias are also found in the flat atrophic mucosa of chronically inflamed colon mucosa , which complicates the macroscopical judgement in the endoscopy. Problems also arise for the pathologist in the separation between inflammatory regenerative epithelatypia and high-grade dysplasia.