Desmoplastic trichoepithelioma with perineural involvement: a series of seven cases.

Desmoplastic trichoepithelioma (DTE) is a benign follicular tumor occurring most commonly within facial skin of young and middle-aged women, morphologically characterized by a superficial dermal proliferation of basaloid cells growing in narrow strands embedded in a desmoplastic stroma associated with small keratinizing cysts. DTE must be distinguished from other benign epithelial proliferations such as syringoma, microcystic adnexal carcinoma and infiltrating basal cell carcinoma. Among morphological features useful in that distinction, perineural involvement is considered a feature indicative of malignancy. We present a series of seven DTEs with otherwise typical presentation and morphology, nevertheless showing epithelium present in the perineural spaces of adjacent small dermal nerves. Patients ranged in age from 14 to 66 years (mean 44 years). All seven tumors were restricted to dermis, showed strands of basaloid epithelium in desmoplastic stroma and contained CK20-positive cells. Additionally, five of five examined tumors displayed diffuse expression of p75 neurotrophin receptor. Five patients were followed up clinically (follow-up time range: 2 months-4 years). No tumor recurrence was observed in any of these patients. We postulate that perineural involvement is an unusual feature of DTE that should not be equated with malignancy or lead to unnecessary over-treatment.