Epithelial cell proliferation, apoptosis, and apoptosis inhibition in inverted papillomas

Inverted papillomas (IPs) are rare benign tumors of nasal epithelium with high recurrence rates and malignant transformation potential. Their etiology is still uncertain, and the mechanism of their growth has not yet been fully described. The purpose of this study was to detect, quantify, and compare cell proliferation, apoptosis, and apoptosis inhibition in hyperplastic epithelium from IPs and in inflammatory nasal polyps (NPs). IP samples were obtained after surgical removal of tumor in 13 patients, and NPs were sampled during endoscopic ethmoidectomy in 10 patients with nasal polyposis. Cell proliferation and apoptosis inhibition, respectively, were assessed by immunohistochemical identification of the proliferating cell nuclear antigen (PCNA) and the oncoprotein Bcl-2. Apoptosis was evaluated by analyzing the DNA fragmentation. Cell proliferation and apoptosis were significantly higher in IPs than in NPs (P = .0002 and P = .043, respectively), while apoptosis inhibition was significantly lower in IPs than in NPs (P = .001). Concerning IPs, cell proliferation was significantly higher than apoptosis (P = .0029) and apoptosis inhibition (P = .0015). The increase in epithelial cell proliferation seemed to be greater in IPs with dysplasia than in IPs without dysplasia. Increased epithelial cell proliferation, but not apoptosis and apoptosis inhibition, seems to be involved in the development of IP.