Desmoplastic trichilemmoma: a case report with immunohistochemical characterization of the extracellular matrix components
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.