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A synovial sarcoma (also known as malignant synovioma) is a rare form of cancer which occurs primarily in the extremities of the arms or legs, often in proximity to and . It is a type of soft-tissue sarcoma.
The name "synovial sarcoma" was coined early in the 20th century, as some researchers 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 tumor develops are unknown and not necessarily synovial. (2025). 155009128X, BC Decker. 155009128X
Primary synovial sarcomas are most common in the soft tissue near the large Joint of the arm and leg but have been documented in most human tissues and organs, including the brain, prostate, and heart.
Synovial sarcoma occurs in about 1–2 per 1,000,000 people a year. They occur most commonly in the third decade of life, with males being affected more often than females (ratio around 1.2:1). (2025). 9780323088343, CV Mosby. ISBN 9780323088343
Like other soft tissue sarcomas, there is no universal grading system for reporting histopathology results. In Europe, the Trojani or French system is gaining in popularity 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. The NCI system is also a three-grade one, but takes a number of other factors into account.
Immunohistochemistry (IHC): SS18-fusion specific antibody and SSX-CT antibody are highly sensitive and specific for synovial sarcoma and when used together may obviate the need for molecular testing in most cases. Cytokeratin is typically expressed, at least focally. TLE1, BCL2 and CD99 may be positive but lack specificity.
The diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18). 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 an SS18-SSX fusion gene. The resulting fusion protein brings together the transcriptional activating domain of SS18 and the transcriptional repressor domains of SSX. It also incorporates into the SWI/SNF chromatin remodeling complex, a well known tumor suppressor. SS18-SSX is thought to underlie synovial sarcoma pathogenesis through dysregulation of gene expression.
There is some association between the SS18-SSX1 or SS18-SSX2 fusion type and both tumour morphology and five-year survival.
Afamitresgene autoleucel (Tecelra) was approved for medical use in the United States in August 2024.
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