[535] Evaluating the Specificity of CD56 as a Neuroendocrine Immunohistochemical Marker

SM Share, M Acon Laws, NT Sherwood, JF Silverman, K Ru. Allegheny General Hospital, Pittsburgh, PA

Background: CD56, an immunohistochemical (IHC) marker that belongs to the family of neural cell adhesion molecules, is widely used in surgical pathology. It is known that CD56 positively stains natural killer cells, activated T-cells, neuroendocrine (NE) tumors, and tissues of the central nervous system. There are multiple NE IHC markers such as NSE, synaptophysin, chromogranin and MAP-2 that are frequently used by pathologists, however the use of CD56 is increasing. In our experience, CD56 appears to be a sensitive NE marker. In this study, we aim to evaluate multiple tumors of various origins in order to determine the specificity of CD56 as a NE IHC marker.
Design: Paraffin embedded surgical specimens of 15 tumor types were retrieved from our files, including 5 cases each of infiltrating ductal breast carcinoma, colonic adenocarcinoma, pancreatic ductal adenocarcinoma (PDA), hepatocellular carcinoma (HCC), transitional cell carcinoma, leiomyosarcoma (LMS), inflammatory pseudotumor, squamous cell carcinoma, Merkel cell carcinoma (MCC), melanoma (MM), paraganglioma (PG), carcinoid tumors of the lung and gastrointestinal tract (CTLG), 6 small cell carcinomas (SCC), and 3 basaloid squamous cell carcinomas. All cases were stained for CD56, synaptophysin, and MAP-2. The slides were reviewed, and staining recorded as negative or strongly, moderately, or weakly positive.
Results: Strong and diffusely positive staining for CD56, synaptophysin, and MAP-2 was seen in 100% of cases of SCC, MCC, PG, and CTLG. MM showed weak to strongly positive staining for all three markers. Weakly positive CD56 staining was noted in a small number of LMS (2/5) and PDA (3/5) cases. CD56 had 100% sensitivity and 78% specificity for NE neoplasms. CD 56 was negative in the other non-NE neoplasms. Synaptophysin and MAP-2 stained weakly to moderately positive in 33% and 44% of non-NE tumors studied, with 67% and 56% specificity, respectively.
Conclusions: CD56, synaptophysin, and MAP-2 all proved to be highly sensitive NE markers. Our results show that CD56 is a highly specific marker with 78% specificity for NE tumors, and is more specific than synaptophysin or MAP-2. The pattern of staining in NE neoplasms appears more intense and diffuse, but the interpretation of CD56 should be approached with caution when evaluating MM, PDA, and LMS. We believe that CD56 is a sensitive and specific IHC marker that should be readily utilized when differentiating NE tumors from other neoplasms.
Category: Endocrine

Monday, March 9, 2009 9:30 AM

Poster Session I Stowell-Orbison/Autopsy Award # 90, Monday Morning