Primary synovial sarcoma of the parapharyngeal space: a clinicopathologic study of five cases.

We report five cases of primary synovial sarcomas arising in the parapharyngeal space. The patients were all men with a median age of 35 years (range 22 to 41 years). The tumors were non-encapsulated solid masses ranging from 2.0 to 6.6 cm in size. Histologically, three cases were biphasic subtype, and the other two cases were monophasic subtype. Immunohistochemically, the tumor cells were strongly positive for bcl-2 and CD99, partly positive for CK and EMA, and negative for CD117, CD34, SMA and desmin in all five cases. S-100 protein was detected in one case. The presence of an SYT-SSX1 and/or SYT-SSX2 gene fusion resulting from t(X;18) was demonstrated from paraffin blocks by reverse transcriptase polymerase chain reaction in five cases. All five patients received tumor radical excision and postoperative radiotherapy, and two patients with pulmonary metastasis received additional chemotherapy. Follow-up data revealed that two patients with tumor size <5 cm were alive without disease for 54 and 57 months, one patient with tumor size <5 cm was alive with pulmonary metastasis for 78 months, and two patients with tumor size >5 cm died of disease 26 and 37 months after the diagnosis, respectively. Primary parapharyngeal synovial sarcoma is a rare variant that occurs more frequently in males than females. Accurate diagnosis depends on morphologic and immunohistochemical examination and proper molecular analysis. The prognosis is relatively good in those patients whose tumor size is less than 5 cm.