Napsin A can be used in a panel to indicate lung origin in a metastatic adenocarcinoma of unknown primary. It has clinical utility for the identification of primary lung adenocarcinomas. Napsin A is also positive in a subset of thyroid and renal cell carcinomas. Napsin A is negative in most squamous cell carcinomas of lung and not been identified in small cell carcinomas. The positive and negative controls are verified as showing appropriate immunoreactivity. Interpretation of this test should be performed in the context of the patient's clinical history and other diagnostic tests by a qualified pathologist.
Napsin A is a promising alternative method, useful to distinguish between lung adenocarcinoma and squamous cell carcinoma. Napsin A test includes only technical performance of the stain and no pathologist interpretation is performed.
Napsin A is expressed in the cytoplasm and is strongly positive in up to 80% of primary lung adenocarcinomas by immunohistochemistry. Less than 5% of assorted adenocarcinomas, including those from the breast, pancreas, biliary tract, and colon stain with Napsin A. Napsin A has also been shown to be useful in the diagnosis of ADC in cell blocks from fine needle aspirates.
Napsin A is a sensitive antibody for identifying adenocarcinoma of pulmonary origin and aids in the identification of primary lung adenocarcinoma. It is also expressed in type 2 pneumocytes, alveolar macrophages and plasma cells; since these cells can be entrapped in tumors, caution must be utilized in determination of true Napsin A reactivity. This antibody should be used in a panel; the combined use of Napsin A and TTF1 (Thyroid transcription factor 1) is associated with increased sensitivity and specificity in identifying pulmonary adenocarcinomas.