title: Polyclonal napsin A expression: a potential diagnostic pitfall in distinguishing primary from metastatic mucinous tumors in the lung.
abstract: BACKGROUND
  Napsin A is a useful marker for distinguishing primary from metastatic lung tumors. Mucinous lung tumors may be difficult to distinguish from metastatic mucinous tumors.
  
  
  OBJECTIVE
  To evaluate napsin A expression in lung and extrapulmonary mucinous tumors on both histology and cytology specimens and to determine napsin A's utility in differentiating primary from metastatic mucinous tumors.
  
  
  METHODS
  Napsin A immunohistochemistry was performed using a rabbit polyclonal antibody on formalin-fixed, paraffin-embedded surgical and fine-needle aspiration biopsy-derived, paraffin-embedded cell block specimens. Positive expression was defined as coarse, granular, cytoplasmic staining in 10% or more of tumor cells.
  
  
  RESULTS
  Sixteen of 32 mucinous lung tumors (50%) and 16 of 33 extrapulmonary mucinous tumors (48%), including 15 of 18 of gastrointestinal origin (83%), expressed napsin A. Positivity was concordant between surgical and cell block specimens in 5 of 9 cases (56%). In 3 of 4 discordant cases, napsin A expression was detected on the surgical specimen but not the cell block. The cell block material in these cases was paucicellular.
  
  
  CONCLUSIONS
  Napsin A shows decreased sensitivity and specificity for mucinous lung tumors and is unlikely to be reliable as a sole immunohistochemical marker of lung origin for such tumors (52% specificity in this study). The high frequency of napsin A expression in gastrointestinal mucinous tumors makes it particularly unreliable in distinguishing metastatic gastrointestinal from primary lung mucinous tumors. However, napsin A expression analysis may facilitate distinguishing mucinous tumors of pulmonary from those of nongastrointestinal origin. Interpretation of napsin A staining may be problematic in mucinous tumor specimens of low cellularity such as cell blocks.
authors: From the Department of Pathology & Laboratory Medicine, NewYork-Presbyterian Hospital-Weill Cornell Medical College, New York, New York.
authors: Jonas J
authors: JJ
authors: Heymann
authors: Rana S
authors: RS
authors: Hoda
authors: Theresa
authors: T
authors: Scognamiglio
mesh_terms: D002288:Adenocarcinoma, Mucinous / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology / Q000556:secondary; D000918:Antibody Specificity; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D044963:Biopsy, Fine-Needle; D003593:Cytoplasm / Q000378:metabolism / Q000473:pathology; D003937:Diagnosis, Differential; D005770:Gastrointestinal Neoplasms / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology / Q000601:surgery; D006801:Humans; D007150:Immunohistochemistry; D008168:Lung / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D008175:Lung Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology / Q000556:secondary; D009363:Neoplasm Proteins / Q000378:metabolism*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D009363:Neoplasm Proteins; D016282:Aspartic Acid Endopeptidases; C498549:NAPSA protein, human