This definition appears rarely
Loss of p27 expression or its reduced level correlates with increased cell proliferation in sinonasal tumours [136, 191]. p27 expression may be associated with keratinization in SCCs of the paranasal sinus and therefore may be a useful marker for the dysregulation of cell kinetics in IP [200–203]. Expression of p21 (waf1/cip1) is associated with terminal differentiation in surface cells in inverted papillomas and cylindrical cell papillomas [136, 203, 204]. Serum SCC antigen may be a useful biologic marker in patients with sinonasal IP [205–207]. Proliferating cell nuclear antigen labeling index.