Nucleolar organizer region enumeration in keratoacanthomas and squamous cell carcinomas of the skin.

Keratoacanthomas (KA) and squamous cell carcinomas (SSC) are epithelial skin tumors exhibiting distinctive clinical and histologic features. However, the differential diagnosis between them in individual cases may be difficult or even impossible. In this article the authors examine the possibility that enumeration of associated proteins of nucleolar organizer regions (AgNOR) could be of help in differentiating KA from SCC. AgNOR counting, performed on unequivocal cases of SCC (n = 20) and KA (n = 16) showed statistically significant higher AgNOR counts in SCC (6.29 +/- 0.91) compared with KA (3.80 +/- 1.62). This result speaks in favor of the different biologic nature of SCC and KA; however, due to significant overlap between the two groups, AgNOR enumeration alone is not sufficiently discriminating so as to be used diagnostically in cases with borderline histologic features.