A case of malignant trichilemmoma produced in solar keratosis by immunohistochemistry dyeing.

A 75-year-old woman had a nodule on her cheek. Histopathological examination revealed lobular proliferaton of clear cells in the center and basaloid in the peripheral area of the tumor. The clear cells were PAS positive, diastase sensitive. The basaloid cells showed palisading. Tumor cells were CEA (-) S-100 (-) . Nuclear atypio was seen. We diagnosed it as a malignant trichilemmoma.Immunohistochemical stining using various monoclonal anticytokeratin antibodies with formalin-fixed and paraffin-embedded block specimans was performed. All the tumor cells were positive to simple epithelial cytokeratin such as CK8, 18. Clear cells were positive to differentiated stratified epithelial cytokeratin such as CK1, and simple epithelial cytokeratin CK19. Staining pattern was different from epidemis, but similar to outer root sheath between is thmus and infundidulum.