Napsin A Expression in Sclerosing Hemangiomas of the Lung.
Lindsay Schmidt, Jeffrey Myers, Jonathan McHugh. University of Michigan, Ann Arbor
Background: Sclerosing hemangiomas (SH) are lung tumors with two distinct cell types: surface cuboidal cells resembling type II pneumocytes, and round stromal cells. SH is now thought to be of primitive respiratory epithelial origin due to its immunohistochemical (IHC) and electron microscopic features. Napsin A, a human aspartic proteinase expressed primarily in type II pneumocytes and alveolar macrophages, is emerging as a helpful IHC marker in characterizing lung neoplasms. We sought to evaluate napsin A staining in SH to help further characterize this unusual tumor.
Design: H&E stained slides from lung resections for SH performed at our institution between 1997-2010 and cases from the authors' consultation files (n=6) were reviewed. IHC was performed using an avidin-biotin-peroxidase complex method on an automated immunostainer (Ventana-Biotech, Tucson, AZ). IHC stains were evaluated for presence of staining, localization of positivity if present, and strength of staining.
Results: Napsin A staining was available for all cases; TTF-1 for 5 cases; cytokeratin (CK) cocktail (CAM 5.2 and AE1/AE3) for 2, CK7 for 1, and CK AE1/AE3 for 1. TTF-1 demonstrated nuclear positivity in both surface and round cells in all 5 cases. CK was positive in surface cells and negative in round cells in all 5 cases. Round cells had focal napsin A staining in 1 case (17%) and surface cells showed positive staining in all 6 cases. In one, surface cell staining was limited to the tumor edge. In one case, most surface cells showed strong granular cytoplasmic staining. In the remaining 4 cases, there were both areas of strong granular staining in surface cells and areas where surface cells were completely negative; negative staining corresponded to weaker keratin expression in these cases.
Conclusions: Similar to others, we observed TTF-1 positivity in both surface and round cells in all SH and CK staining only in surface cells, suggesting primitive respiratory epithelium as the possible cell of origin of SH. Previous reports of surfactant staining in surface, but not in round cells, suggest surface cells are more differentiated than round cells. Our napsin A findings support this, with positivity in surface cells of all tumors (100%), and round cell staining in only one (17%). This suggests that surface cells are type II pneumocytes, which normally express napsin A in a similar granular cytoplasmic pattern. The presence of focal staining in one tumor suggests that round cells may derive from a common progenitor cell. Additional IHC studies on napsin A staining in primitive lung tissue may be of use in further elucidating the origin of SH.
Tuesday, March 1, 2011 9:30 AM
Poster Session III # 274, Tuesday Morning