Synovial sarcoma of the upper digestive tract: A report of two cases with demonstration of the X;18 translocation by fluorescence in situ hybridization

Two cases of synovial sarcoma that arose in the upper digestive tract are r eported. One case was a polypoid mass that arose at the gastroesophageal ju nction; the other was a large intramural mass that arose in the wall of the stomach. Both cases had a classic biphasic pattern. In the stomach tumor, the biphasic morphology was focal and there was an abrupt transition to poo rly differentiated synovial sarcoma, The tumors had immunohistochemical fea tures that were consistent with synovial sarcoma. Ultrastructural evaluatio n of the gastroesophageal tumor supported the diagnosis. The diagnostic X;1 8 translocation was demonstrated by fluorescence in situ hybridization on s ections from paraffin-embedded tissue in 86% and 50% of interphase nuclei f rom the gastroesophageal and gastric tumor, respectively. The translocation was present in equal frequency in the epithelial and spindle cells in the biphasic areas and the poorly differentiated areas of the gastric tumor, in dicating that the development of the more aggressive subclone was probably due to genetic mutations not encompassing the SYT-SSX gene fusion product. We are aware of only five reported cases of synovial sarcoma arising in the digestive tract, all in the proximal esophagus. These cases are the first reported arising in the gastroesophageal junction and stomach and the only cases of synovial sarcoma of the digestive tract in which the diagnostic tr anslocation was demonstrated. Sarcomatoid carcinoma (carcinosarcoma) and ga strointestinal stromal tumor are the main differential diagnoses for synovi al sarcoma in this site. Synovial sarcoma of the digestive tract may be und erdiagnosed, and its recognition may have important clinical implications. Fluorescence kt situ hybridization is helpful in making this distinction.