Background. For the diagnosis of gastric submucosal tumors (SMTs), endoscopic ultrasound (EUS) alone does not reveal the complete pathology, such as the degree of malignancy, and EUS-guided fine-needle aspiration biopsy (EUS-FNAB) has been reported to be more useful. Recently, most cases initially diagnosed as leiomyosarcomas have received further study with immunohistochemical staining and have been given the new diagnosis of gastrointestinal stromal tumors (GISTs). The degree of malignancy of GISTs differs widely in clinical aspects. In this study, we examined whether EUS-FNAB was useful in diagnosing GISTs and differentiating their degrees of malignancy. Methods. From January 1997 to March 2002, 21 cases of gastric GISTs were diagnosed from the immunohistochemical staining of specimens resected at Aichi Cancer Center Hospital. Of these 21 patients, 14 (5 with high-gMe malignancy and 9 with low-grade malignancy) underwent EUS-FNAB preoperatively, and were examined further: their EUS-FNAB specimens were submitted for additional immunohistochemical testing. Results. The EUS-FNAB specimens from all patients were positive for c-kit and CD34 immunohistochemical testing, coinciding with the staining results of the resected specimens. The MIB-1 labeling indices in specimens of high-grade malignancy were significantly higher than those of low-grade malignancy. If we assumed that a tumor with an MIB-1 labeling index of more than 5% was a high-grade malignancy, the diagnostic, accuracy was 85.7%. Conclusions. The EUS-FNAB procedure is a useful tool for diagnosing GISTs of the stomach with immunohistochemical staining. When used with MIB-1 staining, the procedure may indicate GIST prognosis and influence decisions regarding therapeutic strategies.
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