A 30-year-old male presents with a deep thigh mass that he notes has been present for several years. A biopsy section is shown here. What is the diagnosis?

Unknown 25
A. Osteosarcoma
B. Liposarcoma
C. Nodular fasciitis
D. Synovial sarcoma
E. Rhabdomyosarcoma





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The answer is D, synovial sarcoma. The name of this tumor sounds nice and definitive (if it says synovial sarcoma, it must arise from synovium, right?). However, the name just describes the morphologic similarity of the tumor to synovial tissue – it doesn’t mean that the tumor arises from synovial tissue. In fact, the cell of origin is still uncertain.

Synovial sarcomas are rare tumors (they account for about 5-10% of  soft tissue sarcomas, which are themselves rare). Most occur between the ages of 20 and 50. They can occur anywhere, but the most common places are the leg (60%) and arm (20%).

Histologically, synovial sarcomas may be biphasic, monophasic, or poorly-differentiated. The tumor in this particular case is a biphasic synovial sarcoma – it’s composed of spindle cells and epithelial cells. Monophasic tumors can be spindle-cell or epithelial, but they are usually composed of just the spindle cell component.

Synovial sarcomas grow slowly. In fact, many patients describe a several-year history of a mass, which is what you’d expect with a benign tumor. However, synovial sarcoma is aggressive and persistent. Treatment usually involves surgery and chemotherapy, but local recurrence and metastasis are very common. The prognosis is poor, with a 5-year survival between 40-70%.


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