• Cytoplasmic napsin A expression in alveolar (lung) epithelium and alveolar macrophages
  • Napsin A expresion in renal tubules
  • Napsin A positivity in alveolar macrophages
  • Diffuse granular cytoplasmic napsin A expression in a pulmonary adenocarcinoma metastatic to the brain
  • Napsin A in adenocarcinoma of the lung
  • Napsin A in pulmonary adenocarcinoma. Note the granular cytoplasmic staining pattern


Novel Aspartic Proteinase of the PepSIN Family


Technical InfoEdit

Staining PatternEdit

  • Granular cytoplasmic[1]

Expression in Normal TissuesEdit

  • Alveolar epithelium (lung) including type 2 pneumocytes[2]
  • Alveolar macrophages[2]
  • Renal tubules[2]

Expression in Neoplastic EntitiesEdit

Tumor name % Positive Staining Number of Cases
Alveolar adenoma 100% 1/1
Sclerosing hemangioma 100% ("surface cells") 6/6
Intermediate/Uncertain Malignant PotentialEdit
Tumor name % Positive Staining Number of Cases
Tumor name % Positive Staining Number of Cases
Primary adenocarcinoma of lung 83% 79/95
Primary adenocarcinoma of lung 77% 122/158
Thyroid carcinoma
Metastatic adenocarcinoma of lung origin 79% 46/58
Poorly differentiated adenocarcinoma of the lung 58% 11/19

  • Napsin A is expressed in 84.5% of primary lung adenocarcinomas but not in adenocarcinomas of other primary sites[3]

Expression in Non-Neoplastic EntitiesEdit

Pertinent NegativesEdit

This antigen is typically NOT expressed by the following entities:

  • Squamous cell carcinomas of the lung
  • Adenocarcinomas of the GI tract
  • Breast carcinomas of any type

Practical Uses / PanelsEdit

  • Napsin A has been used in a panel with TTF-1, p63 and CK5/6 in small lung biopsies to classify non-small cell carcinomas that lack morphologic differentiating features on H&E. In such cases, napsin A positivity confirms a diagnosis of adenocarcinoma.
  • Napsin A can be used in a panel to indicate lung origin in a metastatic adenocarcinoma of unknown primary.

Common PitfallsEdit

Lung epithelium (napsin A positive) that is entrapped in a napsin A-negative tumor may cause misinterpretation.

Alveolar macrophages (napsin A positive) within a napsin A-negative tumor may cause misinterpretation. Napsin A expression diminishes with decreased differentiation of lung adenocarcinomas.

Napsin A also stains 10% of thyroid carcinomas and renal cell carcinomas.[4]

Related Links/Other ResourcesEdit


  1. 1.0 1.1 Lung Cancer. Volume 41, Issue 2, August 2003, Pages 155-162.
  2. 2.0 2.1 2.2 Arch Histol Cytol. 2002 Oct;65(4):359-68.
  3. Pathology - Research and Practice. Volume 201, Issues 8-9, 10 October 2005, Pages 579-586
  4. Arch Pathol Lab Med. 2008 Mar;132(3):384-96.
Mukhopadhyay S, Katzenstein AL. Subclassification of non-small cell lung carcinomas lacking morphologic differentiation on biopsy specimens: utility of an immunohistochemical panel containing TTF-1, napsin A, p63 and CK5/6. Am J Surg Pathol 2011; 35:15-25.

Bishop JA, Sharma R, Illei PB. Napsin A and thyroid transcription factor-1 expression in carcinomas of the lung, breast, pancreas, colon, kidney, thyroid, and malignant mesothelioma. Hum Pathol. 2010 Jan;41(1):20-5.

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