Diagnosis of Gastrointestinal Stromal Tumors Using Endoscopic Ultrasound Guided Fine Needle Aspiration: The Value of Cellblock and Immunohistochemistry

Abstract

Introduction: Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the gastrointestinal (GI) tract. Their clinical management depends on their risk assessment based on tumor size, location, mitotic count, proliferation index, and histologic grade. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is a common procedure for diagnosing GIST. A recent study reported a discrepancy of immunohistochemical results between the cytology and the surgical resection due to the cytolyte fixation of cytology material. The aim of this study was to analyze our experience on EUS-FNA for establishing diagnosis and malignant risk evaluation of GIST. Methods: A retrospective analysis of adult EUS-FNA of submucosal lesions in the upper GI tract was performed (n=9). Specimens were obtained using a 22 G procore, or a 25 G sharkcore needle from stomach (n=6), duodenum (n=1), esophagus (n=1) and rectum (n=1). Results: The tumor size ranged from 1.3-6.4 cm. All cases yielded sufficient material for cytologic and histological evaluation. Four cases (44.4%) were diagnosed as GIST based on histologic and immunohistochemical findings (positive for CD117 and CD34, negative for desmin, smooth muscle actin, and S-100). One case was classified as high grade, high risk GIST based on mitotic rate (15/5mm2) and high Ki-67 proliferation index (25%). The subsequent resection confirmed the cytology impression. Two cases were classified as low grade and low risk (Ki-67 < 5%). The remaining two cases were diagnostic or suggestive of leiomyomas (n=1, 11.1%) or normal smooth muscle cells (n=1, 11.1%). Conclusion: In this limited sample, EUS-FNA of GI submucosal lesions yielded sufficient material for cellblock preparation and immunohistochemistry to establish the diagnosis of GIST and to perform the evaluation of tumor grade and risk, using either the procore or sharkcore needles. We use formalin as the fixative solution for all cellblock material. There was no discrepancy between the cytology and surgical specimens on CD117 and CD34.