title: Histopathologic assessment of depth of follicular invasion of squamous cell carcinoma (SCC) in situ (SCCis): Implications for treatment approach.
abstract: BACKGROUND
  Squamous cell carcinoma in situ (SCCis) has been reported to involve the hair follicle epithelium. Deep follicular invasion is often cited as a cause of treatment failure.
  
  
  OBJECTIVE
  We sought to define the frequency and the depth of hair follicle invasion by SCCis.
  
  
  METHODS
  The study included both a retrospective review of intraoperative pathology specimens from 42 SCCis cases treated with Mohs micrographic surgery and a prospective evaluation of serially sectioned SCCis tissue from 12 additional patients. Pathology specimens were analyzed for follicular invasion of SCCis.
  
  
  RESULTS
  SCCis invasion of the superficial hair follicle infundibulum was observed in 61.3% to 87.5% of cases in the 2 cohorts, whereas invasion of the isthmus and lower follicle was observed in only 8.3% to 12.5% of cases. In most tumors the depth of follicular invasion was comparable with the thickness of the surrounding epidermis. The maximum observed depth of follicular invasion was 0.82 mm.
  
  
  CONCLUSIONS
  The study was performed on a limited number of cases referred for surgery at a single institution.
  
  
  CONCLUSIONS
  Although SCCis invasion of the upper hair follicle infundibulum is common, deep invasion below the level of the surrounding epidermis is rare. This may have implications for optimal therapy of this condition.
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut. Electronic address: sean.christensen@yale.edu.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Christensen
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: McNiff
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Alicia J
authors.initials: AJ
authors.lastname: Cool
authors.affiliation: Department of Dermatology, Stanford University School of Medicine, Palo Alto, California.
authors.forename: Sumaira Z
authors.initials: SZ
authors.lastname: Aasi
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Hanlon
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: David J
authors.initials: DJ
authors.lastname: Leffell
mesh_terms: D002278:Carcinoma in Situ / Q000473:pathology* / Q000601:surgery; D002294:Carcinoma, Squamous Cell / Q000473:pathology* / Q000601:surgery; D018859:Hair Follicle / Q000473:pathology*; D006801:Humans; D015580:Mohs Surgery; D009361:Neoplasm Invasiveness; D012189:Retrospective Studies; D012878:Skin Neoplasms / Q000473:pathology* / Q000601:surgery
keywords: Bowen disease; Mohs micrographic surgery; adnexal structure; cutaneous; depth; hair follicle; histology; pathology; sebaceous gland; squamous cell carcinoma in situ