Gastric glomus tumor mimicking neuroendocrine tumor on fine needle aspiration: a diagnostic pitfall

Abstract

Abstract Introduction/Objective Glomus tumors (GT) are mesenchymal neoplasms of modified smooth muscle that most commonly affect subungual regions of distal extremities. Although they can occur everywhere in the body, gastric involvement is rare. Gastric GT is usually benign but given the overlapping morphologic and immunohistochemical features with other gastric mesenchymal tumors, GT is commonly misdiagnosed. Methods/Case Report We present two cases of gastric GT initially diagnosed as well-differentiated neuroendocrine tumor (WDNT), G1 on fine needle aspiration (FNA). A 57-year-old female presented with an incidental 1.5 cm gastric submucosal lesion discovered on endoscopy performed for esophageal food impaction. The second case is of a 73- year-old male with a 1.7 cm submucosal lesion found on endoscopy for reflux. Both lesions were located in the gastric antrum. FNA showed clusters of relatively uniform cells with moderate cytoplasm, round nuclei, and stippled chromatin. Tumor cells were focally positive for synaptophysin, while negative for CK7, CD117, DOG-1, and chromogranin. Ki-67 proliferative index was <3%. A diagnosis of WDNT, G1 was made. Subsequent partial gastrectomy showed a submucosal epithelioid neoplasm composed of cells with eosinophilic to clear cytoplasm, and distinct cellular membranes. Focally dilated, tumor-associated thin-walled vessels were noted. Immunohistochemically, the tumor was positive for SMA, calponin, and synaptophysin, and negative for CK AE1/AE3 and chromogranin, supporting the diagnosis of gastric GT. Results (if a Case Study enter NA) N/A Conclusion The rarity of gastric GT, combined with the morphological and immunohistochemical similarity with WDNT, led to diagnostic pitfalls in these cases. With the increased detection and sampling of incidental gastric lesions, cytopathologists should be aware of this uncommon tumor and its mimics, and as such, expand their differential diagnoses.