Quantitation of S100 protein-positive cells in inflamed and non-inflamed keratoacanthoma and squamous cell carcinoma.

Langerhans cells (LC) were identified and quantitated in non-inflamed keratoacanthoma (KA), inflamed KA, non-inflamed squamous cell carcinoma (SCC), and inflamed SCC, by their content of S100 protein. The number of LCs per high-power field was markedly increased in inflamed KA when compared to the other groups. Using similar methods on frozen sections, the expression of HLA-DR was identified on keratinocytes in KA in areas of inflammation but not in other lesions under study. We hypothesize that increased numbers of LCs in inflamed KA are part of the process which results in tumor regression.