Folliculocentric squamous cell carcinoma with tricholemmal differentiation: a reappraisal of tricholemmal carcinoma.

BACKGROUND: The diagnostic criteria for tricholemmal carcinoma remain controversial, and even the existence of tricholemmal carcinoma has been the subject of debate. Follicular (infundibular) squamous cell carcinoma (SCC) is a distinctive subset of SCC, which develops solely with folliculocentricity, and displays the features of conventional SCC without tricholemmal differentiation. AIM: To examine the existence of pure folliculocentric SCCs showing tricholemmal differentiation, that is, tricholemmal carcinoma.
METHODS: In total, 812 SCCs were examined, and those meeting the following diagnostic criteria were selected: (i) pure folliculocentricity without any associated Bowen's disease or actinic keratosis; (ii) composition primarily of lightly eosinophilic cells or clear cells containing glycogen; (iii) columnar lightly eosinophilic or clear cells aligned in a palisade along a discernible basement membrane; (iv) tricholemmal keratinization; (v) glycogen contained within the pale/clear cells; and (vi) cytological atypia and or infiltrative growth. We also evaluated whether the immunohistochemical profile [cytokeratin (CK)1, CK10, CK17, CD34 and D2-40] seen in normal hair follicles was retained in the selected lesions.
RESULTS: Only two lesions met the criteria. The immunohistochemical profile of the normal outer root sheath cells was generally retained in these lesions, except for CD34.
CONCLUSIONS: Tricholemmal carcinoma is a rare occurrence, but it does exist, and at least one type of tricholemmal carcinoma is considered to be related to follicular (infundibular) SCC. © The Author(s). CED