• cytokeratin;
  • immunohistochemistry;
  • trichilemmoma

SummaryBackground The histogenesis of trichilemmoma remains unclear.

Objectives To clarify the histogenesis of trichilemmoma by evaluating its cytokeratin (CK) expression.

Methods In three cases of trichilemmoma, CK expression was studied immunohistochemically using seven antikeratin antibodies against CK1, 10, 14–17 and 19, respectively.

Results CK1 and CK10 were present in keratinizing ductal epithelium. CK14 was present in the whole layer. CK15 was present in suprabasal layers in two cases. CK16 was present in the suprabasal layer, but was absent in keratinizing ductal epithelium. CK17 was present in suprabasal layers and the sebaceous duct-like structure. CK19 was totally absent.

Conclusions These results showed that trichilemmoma may differentiate mainly towards two directions: infundibular keratinization and proliferation of the outer root sheath with undifferentiated and pluripotent characteristics.