The diagnosis of GI stromal tumors with EUS-guided fine needle aspiration with immunohistochemical analysis

Background: With the advent of immunohistochemical analysis, the term "gastrointestinal stromal tumor" (GIST) was proposed to designate the largest category of primary nonepithelial neoplasms. EUS-guided fine needle aspiration (EUS-FNA) is useful for diagnosis of GISTs. The aim of this study was to evaluate the phenotyping of GISTs and diagnosis of malignant GISTs by using EUS-FNA with immunohistochemical analysis. Methods: A diagnosis of GIST was made in 23 patients by using EUS-FNA with immunohistochemical analysis. The accuracy of EUS-FNA diagnosis compared with the EUS imaging alone was analyzed. Additionally, immunophenotyping of specimens obtained by EUS-FNA and surgical resection specimens was compared. Factors that were diagnostic for malignant GISTs were also analyzed. Results: The overall accuracy for the diagnosis of malignant GIST was 78% (18/23) by EUS imaging alone and 91% (21/23) by histopathologic evaluation (H&E staining) of specimens obtained by EUS-FNA. In 21 of 23 cases (91%) the immunohistochemical expressions of c-kit, CD34, muscle actin, and S-100 coincided for the FNA and surgical specimens. The presence of mitotic cells (p = 0.011) and the Ki-67 labeling index (p < 0.0001) with respect to the FNA specimens were significant predictive factors for malignant GIST. For the diagnosis of malignant GIST, the accuracy, sensitivity, and specificity of EUS-FNA with the addition of Ki-67 immunohistochemical staining were 100%. Conclusions: EUS-FNA with immunohistochemical analysis is useful in the preoperative diagnosis of GIST. It provides abundant information on immunohistochemical subtyping and on the capacity of the tumor for cellular progression.