Immunoexpression of napsin a in renal neoplasms

BACKGROUND: Immunohistochemistry (IHC) for napsin A has been widely used to support a diagnosis of lung adenocarcinoma with high sensitivity. In this study, we evaluated immunoreactivity for napsin A in a broad spectrum of renal neoplasms by using tissue microarrays (TMA). METHODS: Duplicate TMA of 159 surgically excised renal neoplasms of various types were constructed. IHC for napsin A was performed on TMAs with appropriate positive and negative controls. RESULTS: Napsin A was expressed in Acquired cystic disease associated renal cell carcinoma (RCC) (2/2, 100.0%), chromophobe RCC (5/45, 11.1%), clear cell RCC (10/23, 43.5%), clear cell papillary RCC (9/19, 47.4%), metanephric adenoma (3/3, 100.0%), oncocytoma (13/23, 56.5%), and papillary RCC (31/37, 83.8%). Expression of napsin A was not seen in mucinous tubular and spindle cell carcinoma (0/1, 0.0%), TFE/MITF RCC 0/1, 0.0%), and urothelial carcinoma (0/6, 0.0%). CONCLUSIONS: Napsin A is expressed in both common and rare sub-types of renal neoplasms with variable sensitivity. Based on our results, napsin A is not specific for lung adenocarcinoma. When a metastatic carcinoma of unknown primary is positive for napsin A, the differential diagnosis should include tumors of both renal and lung origin. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/9558727831304717.