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.
