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Napsin A expression is a valuable marker in small biopsy specimens of nonsmall cell lung carcinoma

Background Accurate subclassification of nonsmall cell lung carcinoma (NSCLC) is crucial for the targeted therapy. In lung cancer, most of the tumors are unrespectable at diagnosis, and a small biopsy or cytological specimen is commonly the only available material for histopathology diagnosis. Although most of NSCLC can be diagnosed by routine stains, diagnosis of poorly differentiated or undifferentiated tumors in small biopsy is challenging. Aim To evaluate the diagnostic value of napsin A immunohistochemical (IHC) marker in NSCLC small biopsy specimens. Patients and methods A total of 46 cases of primary NSCLC diagnosed by biopsy with subsequent resection were enrolled in this study. Subtyping of tumors was done according to 2015 WHO criteria. IHC expression of napsin A was assessed for all the cases. For large cell carcinoma (LCC) cases, thyroid transcription factor 1 (TTF-1) and P63 expression was also tested. Markers expression was correlated with the histological diagnosis of the tumor. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and total accuracy of the markers were calculated. Result In NSCLC cases, the diagnostic sensitivity and specificity of napsin A were 85.2 and 75%, respectively, with PPV of 85.2%, NPV of 75.0%, and 81.4% accuracy. In LCC cases, TTF-1 sensitivity was 57.1%, specificity was 100%, PPV was 100%, NPV was 14.3%, and accuracy was 60.0% In LCC, P63 marker had a diagnostic sensitivity, specificity, PPV, NPV, and accuracy of 100, 85.7, 33.3, 100.0, and 86.7%, respectively. Expression of both napsin A and TTF-1 in LCC cases raised the accuracy to 86.7%. Conclusions In small biopsy specimens, napsin A can subtype NSCLC with high sensitivity and moderate specificity. Additions of TTF-1/P63 IHC markers can further enhance the accuracy.