Proliferating cell nuclear antigen distribution in keratoacanthoma and squamous cell carcinoma

Histologic differentiation of keratoacanthoma (KA) and squamous cell carcinoma (SCC) is often difficult despite well-delineated histopathologic criteria. This has prompted a search for more objective methods to differentiate these two lesions. In the present study, we immunohistochemically examined the distribution of proliferating cell nuclear antigen (PCNA)-positive cells in 11 cases of KA, 7 cutaneous SCC, and 2 atypical squamous proliferations (for which a definitive diagnosis could not be made on routine histology) using a commercially prepared anti-PCNA monoclonal antibody. We found PCNA-positive cells predominantly in the periphery of squamous nests in KA. In contrast, SCC showed a diffuse staining pattern with PCNA-positive cells seen throughout squamous nests. Determining the pattern of PCNA-positive cells is easy, does not require cell counting, and may provide additional histochemical data facilitating the distinction between KA and SCC.