Increased cyclooxygenase-2 expression in large flat colorectal tumors (laterally spreading tumors)

Little is known about the molecular biological features of large flat tumors or laterally spreading tumors (LSTs) of the colon and rectum. The cyclooxygenase (COX)-2 protein expression level of LSTs was assessed immunohistochemically and compared with that of exophytic colorectal tumors. COX-2 expression in the dysplastic epithelial cells and the interstitial cells was evaluated independently. Sixty-five LSTs and 65 exophytic tumors were randomly selected from the archives, and 61 and 59, respectively, were successfully analyzed. LSTs showed significantly more intense COX-2 protein expression in the dysplastic epithelial cells than the exophytic tumors ( P > 0.0001). COX-2-positive interstitial cells were also observed more frequently in LSTs than in the exophytic tumors ( P = 0.015). Overexpression of COX-2 protein may play a crucial role in the tumorigenesis of colorectal LSTs. Chemoprevention, using nonsteroidal anti-inflammatory drugs (NSAIDs) or selective COX-2 inhibitors may be effective for treating this unique neoplasm, which sometimes defies endoscopic treatment.