TRICHOGENIC TRICHOBLASTOMA ARISING ON THE SUPRACLAVICULAR FOSSA WITH AN IMMUNOHISTOCHEMICAL STUDY OF CYTOKERATIN EXPRESSION

We report a 52-year-old female with trichogenic trichoblastoma arising on the supraclavicular fossa. Clinical and histological examinations revealed a thumbnail sized, elastic, hard, subcutaneous nodule which c onsisted of keratinous cysts and epithelial cords of basaloid cells wi th focally follicular differentiation. Based on histological observati ons, a diagnosis of trichogenic trichoblastoma was made. An immunohist ochemical study using a panel of monoclonal antibodies against cytoker atins was performed to investigate the nature and differentiation of t his tumour. The most characteristic findings of the immunohistochemist ry were CK 8 and 19 expression in the epithelial cords and the outer c ells of the cystic structures. These immunoreactivities were similar t o those of the outermost layer of the outer root sheath between the lo wer permanent portion and the upper transient portion, and immunostain ing with the other antibodies confirmed this similarity We can specula te that trichogenic trichoblastoma differentiates mainly toward the ou termost layer of the outer root sheath between the lower permanent por tion and the upper transient portion, and then into follicular structu res.