| Synovial sarcoma | |
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| Classification and external resources | |
Micrograph of a monophasic synovial sarcoma. The histologic appearance is non-specific and overlaps with MPNST and fibrosarcoma. H&E stain. |
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| ICD-O: | M9040/3-9043/3 |
| OMIM | 300813 |
| MeSH | D013584 |
A synovial sarcoma is a rare form of cancer which usually occurs near to the joints of the arm, neck or leg. It is one of the soft tissue sarcomas.
Synovial sarcoma was originally coined early in the 20th century as some thought that the microscopic similarity of some tumors to synovium and its propensity to arise adjacent to joints indicated a synovial origin; however, the actual cells from which the tumour develops are unknown and not necessarily synovial.[1]
Primary synovial sarcomas are most common in the soft tissue near the large joints of the arm and leg but have been documented in most human tissues and organs, including the brain, prostate and heart.
Synovial sarcoma occurs most commonly in the young, representing about 8% of all soft tissue sarcomas[2] but about 15-20% of cases in adolescents and young adults.[3] The peak of incidence is before the 30th birthday and males are affected more often than females (ratio around 1.2:1).[2]
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Two cell types can be seen microscopically in synovial sarcoma. One fibrous type, known as a spindle or sarcomatous cell, is relatively small and uniform and found in sheets. The other is epithelial in appearance. Classical synovial sarcoma has a biphasic appearance with both types present. Synovial sarcoma can also appear to be poorly differentiated or to be monophasic fibrous, consisting only of sheets of spindle cells. Some authorities[1] state that, extremely rarely, there can be a monophasic epithelial form which causes difficulty in differential diagnosis.
Like other soft tissue sarcomas, there is no universal grading system for reporting histopathology results.[4] In Europe, the Trojani or French system is gaining in popularity[5] while the NCI grading system is more common in the United States. The Trojani system scores the sample, depending on tumour differentiation, mitotic index, and tumour necrosis, between 0 and 6 and then converts this into a grade of between 1 and 3, with 1 representing a less aggressive tumour.[4] The NCI system is also a three grade one but takes account of a number of other factors.
Most, and perhaps all, cases of synovial sarcoma are associated with a reciprocal translocation t(x;18)(p11.2;q11.2). There is some debate about whether the molecular observation itself is definitional of synovial sarcoma.[6]
The diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18).[7] This translocation event between the SS18 gene on chromosome 18 and one of 3 SSX genes (SSX1, SSX2 and SSX4) on chromosome X causes the presence of a SS18-SSX fusion gene. The resulting fusion protein brings together the transcriptional activating domain of SS18 and the transcriptional repressor domains of SSX. SS18-SSX is thought to underlie synovial sarcoma pathogenesis through dysregulation of gene expression.[1]
There is some association between the SS18-SSX1 or SS18-SSX2 fusion type and both tumour morphology and five-year survival.[8]
Synovial sarcoma usually presents with an otherwise asymptomatic swelling or mass, although general symptoms related to maligancies can be reported such as fatigue.
Treatment usually involves:
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