The case of unusual desmoplastic variant of trichilemmoma arising in the neck of a 56-year-old man is reported. The tumour was characterized by the presence of a densely sclerotic stroma, surrounded by lobules of epithelial cells with features of outer root sheath differentiation, including glycogen-rich, clear cytoplasm and peripheral palisading. In the central part of the tumour, irregular cords of epithelial cells entrapped in the desmoplastic stroma were found. Differential diagnosis of this rare tumour includes invasive squamous cell carcinoma, morphealike type basal cell carcinoma, desmoplastic trichoepithelioma and desmoplastic trichoblastoma. By immunohistochemistry, the tumour epithelium stained with anti-cytokeratin antibodies while the stromal cells were positive with vimentin. The centro-tumoral extracellular matrix showed a diffuse and intense positivity for type I collagen and tenascin, whereas stains for laminin and type IV collagen were uniformly negative. We suggest that tenascin could be secreted by the epithelial neoplastic cells and play a role in the mesenchymal response, which results in desmoplasia.

Desmoplastic trichilemmoma.Am J Dermatopathol. 1992 Apr;14(2):107-4.

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.