title: Multiply recurrent trichilemmal carcinoma with perineural invasion and cytokeratin 17 positivity.
abstract: BACKGROUND
  Trichilemmal carcinoma is an uncommon cutaneous malignancy that is thought to be the malignant counterpart of the trichilemmoma. Despite histologic features such as pronounced cytologic atypia, trichilemmal carcinoma is often described as having a rather benign clinical course. Cases of tumor recurrence after therapy are uncommon, and tumor neurotropism has never been described.
  
  
  OBJECTIVE
  A case of multiply recurrent trichilemmal carcinoma with perineural invasion is described. The outer root sheath differentiation of this neoplasm is confirmed with the use of novel antibodies directed toward cytokeratins that are expressed in this area of the hair follicle.
  
  
  METHODS
  The trichilemmal carcinoma was excised using the Mohs surgical technique. Tissue obtained during the extirpation of the tumor was subjected to immunohistochemical staining for cytokeratin 15, cytokeratin 17, and c-erb-B2.
  
  
  RESULTS
  Tumor neurotropism was noted. The trichilemmal carcinoma demonstrated abundant cytoplasmic staining for cytokeratin 17 and c-erb-B2.
  
  
  CONCLUSIONS
  In distinction to previous reports, this case reveals that trichilemmal carcinoma can demonstrate significant biological aggression, as reflected by tumor neurotropism and by failure to respond to multiple surgical excisions. The purported outer root sheath differentiation of this neoplasm is confirmed with the use of novel immunohistochemical staining. This immunohistochemical staining may be useful in differentiating trichilemmal carcinoma from other clear cell neoplasms.
authors.affiliation: Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Julie E
authors.initials: JE
authors.lastname: Allee
authors.forename: George
authors.initials: G
authors.lastname: Cotsarelis
authors.forename: Benjamin
authors.initials: B
authors.lastname: Solky
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Cook
mesh_terms: D000368:Aged; D006801:Humans; D007150:Immunohistochemistry; D007633:Keratins / Q000378:metabolism; D008297:Male; D015580:Mohs Surgery; D009361:Neoplasm Invasiveness; D009364:Neoplasm Recurrence, Local / Q000473:pathology*; D010502:Perineum; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000601:surgery
chemical_list: D007633:Keratins