The origins of colorectal carcinoma: specific nomenclature for different pathways and precursor lesions

The widespread application of molecular methods in pathology has yielded steady advances in our understanding of the origins of colorectal carcinoma. Multiple pathways of carcinogenesis have been demonstrated on the molecular level and visualized on the histopathological level. The WHO has accordingly proposed a number of new designations and terms, particularly for precursor lesions, in order to establish a uniform standard for clinical diagnosis. These should be put into practice at once.

In this article, we explain the concept of intraepithelial neoplasia, which replaces the older concept of dysplasia. Moreover, we use this concept in describing a new mechanism of carcinogenesis for colorectal carcinoma, on the basis of a selective review of the literature. We estimate the frequency of precursor lesions according to the new concept using data from our own patient collective. Finally, we discuss the clinical consequences, which have been addressed in the German S3 guideline for colorectal carcinoma.

The new type of precursor lesion, called "sessile serrated adenoma" (SSA), accounts for some 7% of all adenomas in our patient collective and is usually found in the right hemicolon. Traditional serrated adenomas (TSA) made up 1% to 3% of our cases and were found mainly in the left hemicolon and rectum.

Our observations on the frequency and location of serrated adenomas accord with the initial findings published in the international literature. In view of the risk that serrated lesions will progress more rapidly, it is recommended that they should be completely removed, with follow-up at a short interval thereafter (three years according to the German S3 guidelines).