A poorly differentiated synovial sarcoma arising from the pulmonary valve.

Abstract Synovial sarcoma originating in the pulmonary valve is extremely rare. Herein, we report a poorly differentiated synovial sarcoma arising from this peculiar location in a 17-year-old Chinese boy. Histologically, this tumor was entirely poorly differentiated with uniform small round cell morphology, and it exhibited prominent myxoid change in some areas. The diagnosis was confirmed by the presence of SS18 rearrangement and identification of the SS18-SSX1 fusion transcript. To the best of our knowledge, the present case is the first published example of synovial sarcoma occurring in the pulmonary valve. Additionally, this is the first case showing entirely uniform small round cell morphology without classic areas of synovial sarcoma.