title: Laryngotracheal presentation of anaplastic thyroid carcinoma with squamous differentiation: seven cases demonstrating an under-recognized diagnostic pitfall.
abstract: OBJECTIVE
  To describe a series of anaplastic thyroid carcinomas that mimicked primary head and neck squamous cell carcinoma (HNSCC) by virtue of both morphology and clinical presentation.
  
  
  RESULTS
  Seven cases were identified in a 15-year period where a biopsy of an airway lesion that appeared to be squamous cell carcinoma was, in fact, anaplastic thyroid carcinoma. The tumours had squamous and/or spindle cell morphology, with only the squamous component being apparent in the airway biopsy. Some tumours arose within metaplastic (n = 3) or atypical (n = 3) epithelium, supporting the diagnosis of a primary mucosal tumour. Positive PAX8 (n = 5) and TTF-1 (n = 4) staining was identified.
  
  
  CONCLUSIONS
  An endotracheal presentation of anaplastic thyroid carcinoma with squamous morphology may be misdiagnosed as a primary head and neck squamous cell carcinoma. PAX8 and TTF-1 expression are helpful in making the distinction, but the problem lies in suspecting a thyroid carcinoma in what appears to be a straightforward diagnosis of HNSCC.
authors.affiliation: Department of Histopathology, St James Hospital, Dublin, Ireland; Department of Oral and Maxillofacial Surgery, Medicine and Pathology, Dublin Dental University Hospital, Trinity College, Dublin, Ireland.
authors.forename: Mary
authors.initials: M
authors.lastname: Toner
authors.forename: Niamh
authors.initials: N
authors.lastname: Banville
authors.forename: Conrad I
authors.initials: CI
authors.lastname: Timon
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000473:pathology; D004268:DNA-Binding Proteins / Q000032:analysis; D003937:Diagnosis, Differential; D005260:Female; D006258:Head and Neck Neoplasms / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007830:Larynx / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000032:analysis; D000077195:Squamous Cell Carcinoma of Head and Neck; D013194:Staining and Labeling; D065646:Thyroid Carcinoma, Anaplastic / Q000175:diagnosis* / Q000473:pathology; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000473:pathology; D014132:Trachea / Q000503:physiopathology; D014157:Transcription Factors
chemical_list: D004268:DNA-Binding Proteins; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors; C504003:TTF1 protein, human; D014157:Transcription Factors
keywords: airway invasion; anaplastic carcinoma; head and neck squamous cell carcinoma; squamous differentiation; thyroid