title: Napsin A Expression in Anaplastic Lymphoma Kinase-positive Diffuse Large B-Cell Lymphoma: A Diagnostic Pitfall.
abstract: BACKGROUND
  Napsin A is frequently used to classify a tumor of unknown origin as lung primary. Recent studies have shown that Napsin A positivity occurs in adenocarcinomas of nonpulmonary origin such as renal cell carcinomas, endometrial carcinomas, and clear cell carcinomas of ovary. Nonspecific reactivity has been reported with polyclonal Napsin A antibody. On the basis of an index case of anaplastic lymphoma kinase-positive diffuse large B-cell lymphoma (ALK-DLBCL) expressing Napsin A, which was misdiagnosed as poorly differentiated carcinoma of pulmonary origin, we studied Napsin A expression in our archived cases of ALK-DLBCL.
  
  
  METHODS
  A total of 3 cases of ALK-DLBCL were studied for Napsin A immunohistochemistry along with typical immunophenotypic profile of these cases. Archived paraffin-embedded tissue blocks and cytology aspiration smears were used for morphologic interpretation and immunohistochemistry. Rabbit monoclonal Napsin A antibody has been used.
  
  
  CONCLUSIONS
  All 3 cases were positive for Napsin A exhibiting strong cytoplasmic positivity. To the best of our knowledge, expression of monoclonal Napsin A in lymphomas has never been reported. ALK-DLBCL should be considered in the differential diagnosis when evaluating a Napsin A-positive tumor of poorly differentiated morphology and of unknown primary. As Napsin A has not been described in the lymphoid tissue development, the significance of Napsin A positivity in hematolymphoid neoplasms is unknown and warrants further investigation.
authors.affiliation: Department of Pathology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Deepali
authors.initials: D
authors.lastname: Jain
authors.forename: Saumya R
authors.initials: SR
authors.lastname: Mallick
authors.forename: Varsha
authors.initials: V
authors.lastname: Singh
authors.forename: Geetika
authors.initials: G
authors.lastname: Singh
authors.forename: Sandeep R
authors.initials: SR
authors.lastname: Mathur
authors.forename: Mehar C
authors.initials: MC
authors.lastname: Sharma
mesh_terms: D000293:Adolescent; D000077548:Anaplastic Lymphoma Kinase; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D016403:Lymphoma, Large B-Cell, Diffuse / Q000175:diagnosis / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*
chemical_list: C000626173:ALK protein, human; D000077548:Anaplastic Lymphoma Kinase; D020794:Receptor Protein-Tyrosine Kinases; D016282:Aspartic Acid Endopeptidases; C498549:NAPSA protein, human