TRICHOBLASTIC FIBROMA - A CASE-REPORT AND AN IMMUNOHISTOCHEMICAL STUDY OF CYTOKERATIN EXPRESSION

A 47-year-old woman noticed a nodule on her right shoulder that had be en gradually increasing in size without symptoms. Histologic features of the biopsied nodule included round to irregularly shaped epithelial lobules demarcated by abundant sclerotic stroma located within the lo wer dermis and extending to the subcutis. The epithelial lobules consi sted of cuboidal to columnar basaloid cells and were frequently arrang ed in narrow strands with many bifurcations and branching. Cystic stru ctures containing lamellar keratinous material were occasionally found in connection with the lobules. The histologic findings were interpre ted as trichoblastic fibroma. Immunohistochemical studies with antibod ies directed against cytokeratins (CK) and involucrin revealed positiv e staining in most of the tumor cells with RCK102 and 34 beta E12 anti keratin antibodies, whereas the epithelial cords and the peripheral ce lls of the cystic structures stained with 170.2.14, 4.1.18, and CAM 5. 2 antikeratin antibodies. However, CK1 or simple epithelial cytokerati ns were not detected in any neoplastic elements, Based on comparative immunohistochemical findings in normal hair follicles, we propose that trichoblastic fibroma may first differentiate toward the outermost ce ll layer of the outer root sheath between the lower permanent portion and the upper transient portion and then into various other parts of t he hair follicle.