[1887] Analysis of Napsin A Expression in Mucinous Lung Tumors on Histological and Cytological Specimens

Jonas J Heymann, Rana S Hoda, Theresa Scognamiglio. Weill Cornell Medical College, New York, NY

Background: Napsin A is a sensitive and specific marker for lung adenocarcinoma (ADCA) and can be used to distinguish primary from metastatic lung tumors. Mucinous lung tumors may be difficult to distinguish morphologically and immunohistochemically (IHC) from metastatic mucinous tumors. Napsin A expression has not been extensively studied in mucinous lung tumors. In this study, Napsin A expression was evaluated in lung and non-pulmonary mucinous tumors to determine its utility in differentiating primary from metastatic mucinous tumors.
Design: IHC for Napsin A was performed on formalin-fixed, paraffin-embedded surgical specimens or fine needle aspiration biopsy-derived, paraffin-embedded cell block (CB) specimens. Intensity and percentage of positive cells was scored by 2 pathologists as 0 (negative), 1+ (weak), 2+ (moderate), and 3+ (strong). Positive expression (+) was defined as granular, cytoplasmic staining in >10% of cells.
Results: Thirty-four primary mucinous lung tumors were identified from 2005 to 2012, of which 18 (53%) were Napsin A+. Of these, 3 (17%), 10 (56%), and 5 (28%) demonstrated 3+, 2+, and 1+ staining, respectively. Thirty-three non pulmonary mucinous tumors (10 breast, 11 colon, 5 ovary, 5 pancreas, 2 appendix) were evaluated, of which 16 (48%) were Napsin A+. Of these, 1 (6%), 14 (88%), and 1 (6%) demonstrated 3+, 2+, and 1+ staining, respectively. Zero of 10 breast and 1 of 5 ovarian tumors were Napsin A+. The 1 positive specimen showed focal, 2+ staining. Fifteen of 18 gastrointestinal primary tumors (pancreas, colon, and appendix) were Napsin A+. Concordant CB material was available for 11 surgical lung tumor specimens. Napsin A positivity was concordant between surgical and CB specimens in 6 cases (55%, 2 positive and 4 negative). In 3 of the 5 discordant cases, Napsin A expression was detected on the surgical but not the cytology specimen. The CB material in these cases were paucicellular. In 2 of the 5 discordant cases, Napsin A was negative on the surgical specimen and showed diffuse, 1+ staining on the CB.
Conclusions: Napsin A has decreased sensitivity (53% in this study) as an IHC marker of mucinous lung ADCA compared to non-mucinous lung ADCA. Because it may also be expressed by mucinous tumors originating in other sites, it is unlikely to be reliable as a sole IHC marker of lung origin for mucinous tumors (52% specificity in this study), although it may be useful in distinguishing mucinous lung ADCA from mucinous tumors of breast or ovarian origin. Interpretation of Napsin A staining may be problematic in mucinous tumor specimens of low cellularity such as CBs.
Category: Pulmonary

Monday, March 4, 2013 1:00 PM

Poster Session II # 297, Monday Afternoon


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