title: Immunostaining for thyroid transcription factor 1 and cytokeratin 20 aids the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinomas.
abstract: OBJECTIVE
  To study the expression of thyroid transcription factor 1 (TTF-1) and cytokeratin 20 (CK20) in pulmonary small cell carcinomas, extrapulmonary small cell carcinomas, and Merkel cell carcinomas, and thereby determine whether these markers are helpful in distinguishing these 3 groups of small cell neuroendocrine carcinomas.
  
  
  METHODS
  Immunostaining for TTF-1 and CK20 was performed in 102 cases of small cell carcinoma (pulmonary, 52; extrapulmonary, 50) and 23 cases of Merkel cell carcinoma. The results for the 3 groups were compared.
  
  
  RESULTS
  Thyroid transcription factor 1 was expressed in 82.7% of pulmonary small cell carcinomas, 42.0% of extrapulmonary small cell carcinomas (range, 33.3--53.3% for the various sites), and 0% of Merkel cell carcinomas. Cytokeratin 20 staining was consistently negative in pulmonary small cell carcinomas, and positive in 4.0% of extrapulmonary small cell carcinomas and 100% of Merkel cell carcinomas.
  
  
  CONCLUSIONS
  Immunostaining for TTF-1, especially when combined with immunostaining for CK20, can aid in the distinction between Merkel cell carcinoma and small cell carcinoma (both pulmonary and extrapulmonary). However, in individual cases, these markers cannot be used to distinguish between pulmonary and extrapulmonary small cell carcinomas due to the extensive overlap in immunophenotypes.
authors.affiliation: Department of Pathology, Queen Elizabeth Hospital, Hong Kong. cheuk_wah@hotmail.com
authors.forename: W
authors.initials: W
authors.lastname: Cheuk
authors.forename: M Y
authors.initials: MY
authors.lastname: Kwan
authors.forename: S
authors.initials: S
authors.lastname: Suster
authors.forename: J K
authors.initials: JK
authors.lastname: Chan
mesh_terms: D015266:Carcinoma, Merkel Cell / Q000737:chemistry / Q000175:diagnosis*; D018288:Carcinoma, Small Cell / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D004067:Digestive System Neoplasms / Q000737:chemistry / Q000175:diagnosis; D005260:Female; D005833:Genital Neoplasms, Female / Q000737:chemistry / Q000175:diagnosis; D006801:Humans; D007381:Intermediate Filament Proteins / Q000032:analysis*; D053554:Keratin-20; D008175:Lung Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D009687:Nuclear Proteins / Q000032:analysis*; D011471:Prostatic Neoplasms / Q000737:chemistry / Q000175:diagnosis; D012878:Skin Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000473:pathology; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000032:analysis*; D001749:Urinary Bladder Neoplasms / Q000737:chemistry / Q000175:diagnosis
chemical_list: D007381:Intermediate Filament Proteins; C507499:KRT20 protein, human; D053554:Keratin-20; C000614412:NKX2-1 protein, human; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors