Growth patterns of superficially elevated neoplasia in the large intestine

Background: The growth pattern and malignant potential of superficially ele vated neoplastic lesions remain controversial. A flat adenoma is classified as a superficially elevated neoplasm that characteristically demonstrates high-grade dysplasia despite its small size, in contrast, a nodule-aggregat ing (NA) tumor, which consists of multiple small aggregated nodules, can al so be classified as superficially elevated neoplasia. Methods: In this prospective study, 2720 consecutive patients undergoing to tal colonoscopy were examined for superficially for elevated lesions. Clini copathologic characteristics, Ki-ras mutational status, and overexpression of p53 protein were compared in 25 NA tumors and 55 flat adenomas without a central depression (flat tumor). Results: All flat tumors had a tubular pattern, whereas 21 of 25 NA tumors showed a villotubular or tubulovillous pattern. Ki-ras mutation was observe d in 44% of NA tumors but in none of the flat tumors. Overexpression of p53 protein was found in 12% of NA tumors and 7% of flat tumors. Conclusions: NA tumors and flat tumors have different clinicopathologic and genetic characteristics, although both types of tumor are classified as su perficially elevated lesions.