Abstract

A 74-year-old man developed an erythematous plaque on his left cheek in 1985. In 1995, this eruption formed a scaly pigmented irregularly shapen erythematous plaque, 5×8mm in size. The histopathology of the eruption revealed the proliferation of atypical clear cells (PAS+) in the outer root sheath area. The results of a cytokeratin antibody immunohistochemical study were as follows, 34β4 (-), AE3 (+), 34βE12 (+), 35βH11 (-), AE1 (+), 170.2.14 (+) . The reactivity to involucrin was observed in the central area of the tumor. These observations suggest outer root sheath differentiation of this tumor. The cytokeratin study is useful to characterize a malignant trichilemmoma.