title: p75 Neurotrophin receptor differentiates between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma: insights into the histogenesis of adnexal tumours based on embryology and hair follicle biology.
abstract: BACKGROUND
  Tumour development is frequently described in the basic pathology literature as a recapitulation of embryogenesis. However, a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely overlooked. The low-affinity p75 neurotrophin receptor (p75NTR) has a profound role in hair follicle biology. We therefore speculated that it is involved in the histogenesis of follicular adnexal tumours. One of the most challenging diagnoses in dermatopathology is differentiating morphoeic basal cell carcinoma from desmoplastic trichoepithelioma.
  
  
  OBJECTIVE
  To describe the expression pattern of p75NTR during cutaneous embryogenesis, in the adult hair follicle and in morphoeic basal cell carcinoma and desmoplastic trichoepithelioma.
  
  
  METHODS
  Evaluation of the staining pattern for p75NTR was performed using standard immunohistochemical techniques. For comparison, we examined staining for cytokeratin 20 which highlights Merkel cells.
  
  
  RESULTS
  All 17 desmoplastic trichoepitheliomas were immunoreactive with > 80% of the cells stained, whereas 12 of the 14 (86%) morphoeic basal cell carcinomas were p75NTR negative. In the two positive cases of morphoeic basal cell carcinoma < 30% of cells were labelled. In the late bulbous hair peg stage and in the postnatal anagen hair follicle p75NTR highlights the outer root sheath.
  
  
  CONCLUSIONS
  Our results support the classification of desmoplastic trichoepithelioma as a follicular hamartoma mimicking the outer root sheath. In contrast, the lack of p75NTR expression in morphoeic basal cell carcinoma favours a concept of this tumour as a more primitive follicular lesion with the characteristics of a carcinoma and not a hamartoma. We suggest including p75NTR as a tool in the differential diagnosis between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma.
authors.affiliation: Institut für Dermatohistologie, Heidelberg, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Krahl
authors.forename: K
authors.initials: K
authors.lastname: Sellheyer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002280:Basal Cell Carcinoma / Q000196:embryology / Q000378:metabolism* / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D018859:Hair Follicle / Q000378:metabolism*; D006801:Humans; D008297:Male; D018862:Merkel Cells / Q000378:metabolism; D008875:Middle Aged; D018294:Neoplasms, Adnexal and Skin Appendage / Q000196:embryology / Q000378:metabolism* / Q000473:pathology; D020800:Receptor, Nerve Growth Factor / Q000378:metabolism*; D012867:Skin / Q000196:embryology / Q000378:metabolism; D012878:Skin Neoplasms / Q000196:embryology / Q000378:metabolism* / Q000473:pathology
chemical_list: D014408:Biomarkers, Tumor; D020800:Receptor, Nerve Growth Factor