Applications and Limitations of Immunohistochemical Expression of “Napsin-A” in Distinguishing Lung Adenocarcinoma From Adenocarcinomas of Other Organs

Abstract

Distinguishing between primary lung adenocarcinoma and metastatic adenocarcinoma of lung before planning patient treatment is clinically important. Immunohistochemical markers play an important role in classification of primary lung tumors and are an effective method for separating metastatic tumors from primary pulmonary carcinoma. In this study, we evaluated the expression of Napsin-A in primary pulmonary carcinoma and some cases of nonpulmonary adenocarcinoma. The Napsin-A immunohistochemical evaluation was carried out using surgical specimens from 18 cases of adenocarcinoma, 19 cases of squamous cell carcinoma, 2 cases of large cell carcinoma, 1 case of bronchoalveolar carcinoma of lung, as well as 33 cases of renal cell carcinoma, 30 cases of thyroid neoplasm, 31 cases of colonic carcinoma, 31 cases of breast carcinoma, and 30 cases of endometrial adenocarcinoma. For the primary lung carcinoma cases, all 18 cases of adenocarcinoma, 2 of the large cell carcinomas, and the 1 bronchioloalveolar carcinoma case were positive for Napsin-A. For the thyroid tumors, Napsin-A was positive in 14 cases of papillary carcinoma. Napsin-A was positive for 87.5% of papillary renal cell carcinoma cases and in 29.4% of clear cell carcinoma cases and for 1 chromophobe renal cell carcinoma case. Three out of 30 endometrial adenocarcinomas showed Napsin-A reactivity. All squamous cell carcinoma cases and adenocarcinomas of colon and breast were negative for Napsin-A. Napsin-A is a useful marker for differentiating primary lung adenocarcinoma from squamous cell carcinoma. However, Napsin-A immunoreactivity has the potential to misguide a pathologist to conclude a metastasis from renal, thyroid, or endometrial carcinoma as a primary lung adenocarcinoma. Therefore, when there is a need to rule out lung metastasis from other organs, implementation of other biologically specific markers should be considered.