Synovial Sarcoma of the Stomach: A Clinicopathologic, Immunohistochemical, and Molecular Genetic Study of 10 Cases

Only a few synovial sarcomas arising in the gastrointestinal tract have been reported, most of them are from the esophagus. We report clinical, histopathologic, and immunohistochemical features of 10 gastric synovial sarcomas. These tumors occurred in 4 males and 6 females with mean and median age of 52 years (range, 29 to 68 y). None of the patients had evidence of synovial sarcoma elsewhere. The tumor sizes ranged from 0.8 to 15 cm (mean, 3 cm). Two tumors were large transmural masses of 8 and 15 cm, and 8 were 0.8 to 6 cm, ulcerated cuplike or plaquelike or oval lesions predominantly involving the luminal side. Histologically, 9 tumors were monophasic one also having a poorly differentiated round cell component, and one was biphasic. Microscopic calcifications were present in 2 tumors. At least focal keratin (AE1/AE3 cocktail, keratin 7) and/or epithelial membrane antigen-positivity were detected in all tumors, and there was no CD34 or KIT-immunoreactivity. SYT-SSX fusion transcripts were demonstrated in 7 cases studied by a polymerase chain reaction-based fusion transcript assay. Five patients had a partial gastrectomy, and 5 underwent wedge or segmental resections. Two patients had received chemotherapy after surgery, but none had postoperative radiation. Four patients with plaquelike or cuplike tumors ≤3 cm were alive and well 1, 2, 2, and 18.5 years after surgery. Two patients died of tumor 25 and 29 months after surgery. One of them had a large 8-cm tumor, and another had a 2-cm tumor with a poorly differentiated component. Two patients were alive with recurrences 6 and 48 months after diagnosis. Synovial sarcoma rarely occurs as a gastric primary tumor. It has a variable prognosis depending on tumor size and differentiation, and should be considered in the differential diagnosis of KIT-negative gastric spindle cell neoplasms.