[395] DOG1: Utility in Diagnosing Gastrointestinal Stromal Tumors on Fine Needle Aspiration.

Richard Kraus, Cynthia Cohen, Momin T Siddiqui. Emory University Hospital, Atlanta, GA

Background: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the GI tract, and the majority contain KIT or PDGFRA activating mutations. Fine needle aspiration biopsy (FNAB) is a valuable tool in the diagnosis of GIST, and may allow for pre-operative therapy with tyrosine kinase inhibitors (TKI). Because of the morphologic diversity of these tumors, routine diagnosis of GIST often relies on C-Kit immunohistochemical staining in addition to morphologic findings. However, up to 15% of GISTs are C-Kit negative. Antibodies with increased sensitivity and specificity for detection of C-Kit negative GIST cases could be of value, especially since some of these cases may also benefit from TKI therapy.
Design: Immunohistochemical staining for DOG-1, C-kit (CD117), and protein kinase C theta (PKCθ) was performed on FNA cell block preparations representing 18 GISTs, 17 leiomyosarcomas, 16 melanomas, 16 schwannomas and 11 adenoid cystic carcinomas (ACC).

DOG-118/18 (100%)0/17 (0%)0/16 (0%)0/16 (0%)0/11 (0%)
C-Kit13/18 (72.2%)1/17 (5.9%)4/16 (25%)0/16 (0%)10/11 (90.9%)
PKCθ6/18 (33.3%)1/17 (5.9%)5/16 (31.6%)0/15 (0%)1/10 (10%)

DOG-1 was found to have 100% sensitivity and 100% specificity in diagnosis of GIST. C-Kit demonstrated 72.2% sensitivity and 75.0% specificity, and PKCθ showed 33.3% sensitivity and 88.3% specificity. When only spindle cell neoplasms were considered (adenoid cystic carcinomas excluded), the specificity of C-Kit increased to 91.7%. Of interest, all C-Kit negative cases showed DOG-1 positivity.
Conclusions: DOG-1 is the most sensitive and specific of the three markers for the diagnosis of GIST in cell blocks, and may be of particular use in the diagnosis of C-Kit negative GIST. In addition, DOG-1 helps in differentiating GIST from neoplasms such as ACC and melanomas which have a high incidence of C-Kit positivity, and may be challenging in cases of metastatic disease.
Category: Cytopathology

Monday, February 28, 2011 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 50, Monday Morning


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