[398] Napsin-A Expression in Small Cell Carcinoma of the Lung: A Cytologic Study.

Scott R Lauer, Cynthia Cohen, Michelle D Reid. Emory University Hospital, Atlanta, GA

Background: Napsin-A is an aspartic proteinase involved in surfactant protein B maturation. It is overexpressed in pulmonary adenocarcinomas (PA), and is a useful diagnostic alternative to thyroid transcription factor-1 (TTF-1). TTF-1 is also expressed by small cell carcinoma of the lung (SCCA) and facilitates its diagnosis. While Napsin-A expression has been examined in PA and pulmonary squamous cell carcinoma, its expression in SCCA of lung has not been fully evaluated. We examined Napsin-A expression in 36 cytologically confirmed cases of SCCA to determine if its expression paralleled that of TTF-1. To date ours is the largest cytologic series of lung SCCAs examined for Napsin-A expression.
Design: Thirty-six (36) primary and metastatic SCCAs diagnosed on fine needle aspiration (FNAB) or pleural effusion, with corresponding cell blocks, were identified. Patients ranged in age from 43 – 87 years (mean 57 years) with 20 males and 16 females. FNABs of mediastinal masses (n=5), liver masses (n=3), a subcutaneous nodule (n=1), lung masses (n=6), axillary, cervical and mediastinal lymph nodes (n=20) and 1 pleural effusion were immunostained with Napsin-A, TTF-1, pancytokeratin and at least one of three neuroendocrine (NE) markers (synaptophysin, chromogranin, CD56).
Results: The immunohistochemical results are summarized in Table 1.

Napsin-A, TTF-1 and Neuroendocrine Marker Expression in Small Cell Carcinoma of Lung (n=36)

Result	Napsin-A	TTF-1	Synaptophysin	Chromogranin	CD56	Pancytokeratin
Positive	0 (0%)	35 (97%)	29 (81%)	17 (47%)	23 (64%)	35 (97%)
Negative	36 (100%)	1 (3%)	3 (8%)	10 (28%)	1 (3%)	0 (0%)
Not Tested	0 (0%)	0 (0%)	4 (11%)	9 (25%)	12 (33%)	1 (3%)

All 36 cases (100%) of SCCA were Napsin-A negative. Napsin showed focal positivity in macrophages as well as type II pneumocytes. All 36 (100%) cases expressed at least one or more NE marker; 35/36 (97%) were pancytokeratin-positive and 35/36 (97%) TTF-1 positive. The TTF-1-negative SCCA was positive for NE markers and pancytokeratin and showed cytomorphologic features of SCCA.
Conclusions: While Napsin-A is frequently expressed in PA it is almost never expressed by SCCA of the lung. Therefore, Napsin-A should not be used in the cytologic diagnosis of SCCA, other than as an exclusionary parameter. However, in situations where it is cytologically challenging to differentiate SCCA from PA (especially since both are TTF-1-positive), a positive Napsin-A would favor PA, and would therefore prove useful in distinguishing the two. Larger studies are needed to examine Napsin-A expression in other NE lung tumors.
Category: Cytopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 82, Tuesday Morning