Napsin A

Napsin A is a cytoplasmic aspartic protease involved in maturation of prosurfactant protein B and is normally expressed in type II pneumocytes, alveolar macrophages, renal tubules, and pancreatic ducts. In IHC it shows granular cytoplasmic staining and is most commonly used to support the diagnosis of primary lung adenocarcinoma, where it is usually positive, as well as clear cell carcinomas of the gynecologic tract, which may show focal or rare positivity. Because it is typically negative in the majority of these tumours, Napsin A is highly valuable in tumour histotype classification, particularly of lung and gynecologic clear cell lesions (1).

Recommended Controls

Criteria for acceptable staining is a granular cytoplasmic staining pattern. Recommended control to include is normal colon and a colon tumour which is a negative and for a positive control. Normal lung will show moderate granular cytoplasmic staining of virtually all type II pneumocytes as well as alveolar macrophages and lung tumour will show strong positive staining in all tumour cells including type II pneumocytes and alveolar macrophages.

Expected staining pattern

Lung adenocarcinoma

Normal lung

Normal colon

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.