Desmoplastic trichilemmoma.

Seven cases of desmoplastic trichilemmoma (DT), a recently described pseudomalignant variant of trichilemmoma, are reviewed. The tumor generally occurs in men after the fifth decade of life and presents as a small solitary nodule on the face. It is frequently misdiagnosed clinically as a basal cell carcinoma or a papilloma. Histologically DT displays a superficial lobular growth arranged about a central prominent desmoplastic stroma. At the periphery, the tumor lobules show the typical features of trichilemmoma. In contrast, at the center the cells assume a more random pattern of cords and strands traversed by the hyaline stroma, mimicking invasive carcinoma. The tumor's architectural pattern, in particular the perilobular hyaline mantle, enables DT to be differentiated from basal cell carcinoma and malignant trichilemmoma. Immunohistochemical analysis failed to demonstrate human papilloma virus (HPV), epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), and alpha-lactalbumin in tumor epithelium. Keratin was expressed by the central pseudoinvasive epithelial cords. Neither factor XIIIa nor keratin expression was found in the stromal cells, which stained only for vimentin. These findings suggest that DT is not an HPV-induced epithelial proliferation and that the stroma is not the result of degenerative changes in tumor epithelium. Instead, there appears to be a fibroblast-mediated, dendrocyte-independent, stromal reaction producing this appearance.