RESUMEN
The objective was to evaluate the differentiation of keratoacanthoma from squamous cell carcinoma by using argyrophilic nucleolar organizer region staining. Thirty one cases of keratoacanthoma and 31 cases of squamous cell carcinoma [S.C.C] were selected. The AgNOR staining carried out. Counting of AgNOR was done in 100 cells of each tumor. Two criterias including M.AgNOR [mean number of AgNORs] and P.AgNOR [percentage of nuclei with five or more than five AgNORs per nucleous] were used. Statistical analysis was done by Mann- Whitney test. Significant increase in M.AgNOR and P.AgNOR was found in S.C.C compared with keratoacanthoma [M.AgNOR =16.52 +/- 10.1 and P.AgNOR = 84.12 +/- 23.4 in S.C.C compared with M.AgNOR = 6.58 +/- 4.4 and P.AgNOR = 52.29 +/- 26.7 in keratoacanthoma, P=0.000]. Exceptionally overlapping was seen. This study indicated that the AgNOR counting is a valuable diagnostic criterion for differentiation of keratoacanthoma and S.C.C especially in cases with borderline histologic features