Background: GI stromal tumors are spindle cell tumors that stain positive for immunohistochemical CD-117 (c-kit). Prognostic factors for malignancy include size (>4 cm), mitotic index (5 mitotic figures/50 high-powered fields), and ulcerated, cystic, or necrotic areas within the tumor. The purpose of this study was to compare these features in c-kit positive vs. c-kit negative tumors. Methods: All patients referred for EUS of submucosal lesions were identified, and histopathology, including immunohistochemical staining, was reviewed to determine all diagnoses of GI stromal tumors. Size, echo pattern, and presence of cystic spaces and ulceration were recorded as diagnosed by EUS. Histopathologic diagnoses were made by FNA or endoscopic submucosal-mucosal resection. If surgical resection followed, the surgical diagnosis, staining pattern, mitotic index, and presence of ulceration, necrosis, and nuclear atypia were recorded. Results: Forty patients (21 men, 19 women; 38 white, 2 African American; mean age 58 ± 2.6 years) had 46 EUS procedures performed for evaluation of spindle cell tumors. Seventeen stained positive for c-kit (mean age, 59 ± 3.6 years; range 19 to 80 years) and 12 negative (mean age, 57 ± 3.8 years; range 31 to 76 years); 11 were not stained for c-kit (excluded from analysis). On EUS, 7 were ulcerated, 3 cystic, and 6 were larger than 4 cm. This group of findings was observed in 12 patients, 11 of whom had c-kit positive tumors (11/17 vs. 1/12; p = 0.006). Tumors positive for c-kit were larger (42.4 ± 5.5 mm vs. 19.0 ± 5.9 mm; p = 0.005). There were 13 c-kit positive tumors in the stomach, 2 in the duodenum, and 1 each in the esophagus and at the gastroesophageal junction. Of the 12 c-kit negative tumors, 8 were located in the esophagus and 1 at the gastroesophageal junction (9/12 vs. 2/17; p < 0.01). Surgical resection was performed on 13 patients, 12 of whom had c-kit positive tumors, and 3 of these 12 tumors had greater than 5 mitoses per 50 high-powered field. Conclusions: If a GI stromal tumor is suspected, EUS-FNA with immunohistochemical staining should be performed for CD-117 (c-kit). C-kit tumors are more likely to have malignant features and should be resected or subjected to close clinical follow-up.
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