Intraepithelial elastic fibers and intracytoplasmic glycogen: diagnostic aids in differentiating keratoacanthoma from squamous cell carcinoma.

A significant statistical difference was found between the incidence of intraepithelial elastic fibers in keratoacanthoma and squamous cell carcinoma arising in actinic keratosis (P < 0.001). There was no significant difference when keratoacanthoma was compared to adenoid squamous cell carcinoma (P = 0.13) and de novo squamous cell carcinoma (P = 0.73). However, in keratoacanthoma intraepithelial elastic fibers were found in areas of pseudoepitheliomatous hyperplasia and in the central keratin plug, as well as in areas of infiltrating, peripheral keratinocytes. In adenoid squamous cell carcinoma and de novo squamous cell carcinoma, the intraepithelial elastic fibers were found only in areas of atypical epithelial cells at the margin of the neoplasm. Intracytoplasmic glycogen was found to be statistically more abundant in keratoacanthoma than in squamous cell carcinoma arising in actinic keratosis (P < 0.001), adenoid squamous cell carcinoma (P < 0.001), and in de novo squamous cell carcinoma (P < 0.001)