Patterns of p21 expression in non-papillomatous nasal mucosa, endophytic sinonasal papillomas, and associated carcinomas

Aims—To clarify p21 expression in sinonasal lesions. Methods—Archived surgical specimens from 38 patients were investigated by means of immunohistochemistry. p21 staining was evaluated in the diVerent layers of the epithelium. In addition, human papillomavirus (HPV) infection and p53 protein overexpression were assessed and correlated with p21 expression. Results—p21 staining was negative in non-papillomatous nasal mucosa. HPV infection and p53 protein overexpression were not seen. Sixteen of 20 inverted papillomas showed p21 expression. HPV infection was found in 16 cases and p53 protein overexpression was present in 13 specimens. Expression of p21 was restricted to surface cells in five cases, but involved basal/parabasal cells in 11 specimens. Immunoreactivity for p21 in basal/parabasal cells colocalised with p53 protein overexpression. Enhanced expression rates for p21 were seen in transitional and squamous epithelium compared with columnar epithelium. p21 expression involved only surface cells in cylindrical cell papillomas. HPV infection and p53 protein overexpression were detected in all specimens. One of five squamous cell carcinomas showed p21 expression. HPV infection was seen in two cases, and all carcinomas showed p53 protein overexpression. Conclusions—Expression of p21 is associated with terminal diVerentiation in surface cells in inverted papillomas and cylindrical cell papillomas, but not in non-papillomatous nasal mucosa. Overexpression of p53 protein colocalises with p21 expression in basal/parabasal cells in inverted papillomas but not in cylindrical cell papillomas. Expression of p21 in squamous cell carcinomas involves a subset of tumours with p53 protein overexpression. (J Clin Pathol 2001;54:871–876)