[1794] Napsin A Is Frequently Expressed in Pulmonary Adenocarcinoma but Rarely Detected in Neuroendocrine Tumors of the Lung

JJ Findeis-Hosey, Q Yang, LA McMahon, F Li, H Xu. University of Rochester Medical Center, Rochester, NY

Background: Napsin A is an aspartic proteinase that is involved in the maturation of surfactant B protein. Napsin A has been shown to be highly expressed in pulmonary adenocarcinoma and papillary renal cell carcinoma and occasionally detected in thyroid carcinoma. There are only a few reported cases of carcinoids and small cell lung carcinomas (SCLCs) that were immunohistochemically studied with Napsin A. The aim of this study was to determine if neuroendocrine tumors of the lung (NETL), including typical carcinoid (TC), atypical carcinoid (AC), large cell neuroendocrine carcinoma (LCNEC) and SCLC, immunohistochemically express Napsin A.
Design: Forty-six surgically resected NETL including 14 TCs, 12 ACs, 11 LCNECs, and 9 SCLCs and a tissue microarray of 148 cases of adenocarcinoma of the lung were immunohistochemically studied using a monoclonal antibody against Napsin A (Leica). Cytoplasmic staining was considered positive. The percentage of positively stained tumor cells was recorded and the staining intensity was graded as weak, moderate, or strong. A case was considered positive if more than 5% of tumor cells had staining. Pathologic diagnosis was confirmed, with the use of prior immunohistochemical and mucicarmine stains. A p value of <0.05, as determined by two-tailed Fisher exact test, was considered statistically significant.
Results: Immunohistochemical studies showed all 12 cases of AC and all 9 cases of SCLC were negative for Napsin A staining. There was positive Napsin A staining in 1 (7.1%) of 14 TCs, with only weak staining in 30% of cells. There was positive Napsin A staining in 1 (9.1%) of 11 cases of LCNEC, with diffuse and strong positivity in greater than 90% of tumor cells. Napsin A positivity was detected in 126 (85.1%) of 148 cases of lung adenocarcinoma, including 23 (88.5%) of 26 well-differentiated, 68 (90.7%) of 75 moderately-differentiated and 35 (74.5%) of 47 poorly-differentiated adenocarcinomas. In non-neoplastic lung, Napsin A staining was present in type II pneumocytes.
Conclusions: Napsin A is rarely expressed in NETL. In contrast, it is expressed in a majority of pulmonary adenocarcinomas. These findings support the concept that the cell origins of adenocarcinoma and NETL are different. In addition, immunohistochemical detection of Napsin A expression may serve as a useful diagnostic tool in the distinction between NETL and poorly-differentiated pulmonary adenocarcinoma, in particular when the diagnostic tissue is limited in a small biopsy with a crush artifact.
Category: Pulmonary

Wednesday, March 24, 2010 9:30 AM

Poster Session V # 245, Wednesday Morning


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