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 joint capsules and tendon sheaths.

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.

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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).

Signs and symptoms

Synovial sarcoma usually presents with an otherwise asymptomatic swelling or mass, although general symptoms related to malignancies can be reported such as fatigue.

Diagnosis

The diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18) chromosomal translocation. 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. Cytokeratin is typically expressed, at least focally. TLE1, BCL2 and CD99 may be positive but lack specificity.

Molecular biology

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 definitive of synovial sarcoma.

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.

Treatment

Treatment is usually multimodal, involving surgery, chemotherapy and radiotherapy:

  • Surgery, to remove the tumor and a safety margin of healthy tissue. This is the mainstay of synovial sarcoma treatment and is curative in approximately 20–70% of patients, depending on the particular study being quoted.
  • Conventional chemotherapy, (for example, doxorubicin hydrochloride and ifosfamide), to reduce the number of remaining microscopic metastases.
  • Radiotherapy to reduce the chance of local recurrence.

References

  • Sarcoma Help: What is Synovial Sarcoma?
  • WebMD: Synovial Sarcoma Overview