Classification of Colon Polyps and Risk of Neoplastic Progression

Colorectal polyps are small clumps of cells and they are classified on the basis of their histological characteristics. Until recently, they have been divided into two major groups: neoplastic and non-neoplastic mucosal polyps. Adenomatous polyps contain epithelial neoplasia and their size and histology correlate with the risk of progression to carcinoma. Non-neoplastic polyps, instead, can be divided into several distinct and unrelated categories including hyperplastic, mucosal, juvenile, Peutz-Jeghers, and inflammatory. Adenomas are recognized as the precursor lesions for colorectal carcinoma and recently also some hyperplastic lesions, with serrated morphology, have been reported to display a significant risk of neoplastic progression through the so-called serrated pathway. The sequence adenoma-carcinoma is caused by different molecular pathways. The most frequent are those of chromosomal instability pathway; the microsatellite instability pathway; the serrated pathway. Molecular complexity can explain the morphological heterogeneity and the timing of neoplastic progression.