Gastric glomus tumor on EUS-FNA-based cytology: clinicopathologic and immunohistochemical features of 4 cases, including 1 case with associated MIR143HG-NOTCH2 fusion gene.

INTRODUCTION:Gastric glomus tumor (GT) is a rare submucosal tumor for which the preoperative diagnosis can be challenging. We report the cytomorphologic and immunohistochemical features of 4 gastric GTs diagnosed by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) cytology. MATERIALS AND METHODS:Files were searched to identify gastric GTs diagnosed by EUS-FNA between 2018 and 2021. A total of 4 cases of gastric GTs (3 men and 1 women; mean age, 60 years) were included. RESULTS:Three GTs were located in the gastric antrum and one in the gastric body. Their size ranged from 2 to 2.5 cm. Three patients presented with epigastric discomfort and one with chest wall discomfort. Rapid on-site evaluation was performed for 3 cases; the findings for all 3 were indeterminate. The smears were moderate to highly cellular and showed loose clusters of evenly distributed small- to medium-size bland tumor cells. The tumor cells had centrally located round to oval nuclei with inconspicuous nucleoli and scant to moderate amount of eosinophilic to clear cytoplasm. Examination of the cell blocks revealed branching small vessels surrounded by small- to medium-size cells. The neoplastic cells were positive for smooth muscle actin and synaptophysin and negative for AE1/AE3 and S-100. C-KIT and CD34 were variably positive. Ki-67 was <2% positive. In 1 case, the fusion panel-solid tumor (50 genes) revealed the MIR143HG-NOTCH2 fusion gene. CONCLUSIONS:Smears and cell block preparation revealed angiocentric sheets of uniform, small round to oval tumor cells with pale to eosinophilic cytoplasm, intermingled with endothelial cells. The differential diagnosis of gastric GTs on rapid on-site evaluation includes neuroendocrine tumors and epithelioid or spindled cell neoplasms. Immunohistochemical and molecular studies can be helpful in the preoperative diagnosis of gastric GT.