[1757] Immunoreactivity of Napsin A in Non-Lymphoid Tumors of Anterior Mediastinum, a Comparative Study with TTF-1.

Pil Gyu Hwang, Leslie A Litzky, Paul J Zhang. Hospital of the University of Pennsylvania, Philadelphia

Background: Of the non-lymphoid tumors, primary pulmonary carcinoma, thymoma and germ cell tumor are among the tumors most commonly encountered in anterior mediastinum. Although these can be usually differentiated by their morphologic characteristics, diagnosis can be difficult in certain circumstance such as limited material. In such case, TTF-1 reactivity would strongly favor a lung primary vs. others. Napsin A is a new immunohistochemical marker that is known to be positive in >80% of pulmonary adenocarcinoma. However, napsin A has not been extensively studied in other commonly encountered mediastinal tumors such as thymoma and germ cell tumor. In attempt to better understand its utility in the differential diagnosis of tumors of anterior mediastinum, we evaluated napsin A in thymoma and germ cell tumor and compared it that of TTF-1.
Design: A total of 37 cases of thymoma of various types and 22 cases of germ cell tumor were retrieved from the Surgical Pathology of the Hospital of the University of Pennsylvania and Presbyterian Medical Center. Napsin A (KCG1.1, 1:100, Abcam) and TTF-1 (8G7G3/1, 1:100, Dako) immunostains were performed on representative section of each case with standard immunohistochemical method.
Results: Of 37 thymomas, two (5.4%) showed focal faint positive napsin A reactivity and one (2.7%) showed focal weak nuclear TTF-1 reactivity. Napsin A and TTF-1 were each focally positive in two (9.1%) of 22 cases of germ cell tumor. In these unusual positive cases, the tumors were mixed germ cell tumor and immunoreactivity of either napsin A or TTF-1 was detected in well-differentiated glandular structures of the teratomatous component in the tumor.
Conclusions: Our finding of rare TTF-1 reactivity in thymoma and germ cell tumor are consistent with that of the prior studies. Similar to TTF-1, we also found that napsin A is also focally positive in rare thymoma and germ cell tumor. In germ cell tumor, focal expression of both markers is typically limited to better differentiated glandular element in the teratomatous area. Positive staining of either of these two markers would make the diagnosis of thymoma or germ cell tumor very unlikely and can be used to confirm a lung primary in the differential diagnosis of an anterior mediastinal tumor.
Category: Pulmonary

Monday, February 28, 2011 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 230, Monday Morning


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