Asynovial sarcoma (also known asmalignant synovioma[1]) is a rare form ofcancer which occurs primarily in the extremities of the arms or legs, often in proximity tojoint capsules andtendon sheaths.[2] It is a type ofsoft-tissue sarcoma.
The name "synovial sarcoma" was coined early in the 20th century, as some researchers thought that the microscopic similarity of some tumors tosynovium, 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.[3]
Primary synovial sarcomas are most common in thesoft tissue near the largejoints of the arm and leg but have been documented in most human tissues and organs, including thebrain,prostate, andheart.
Synovial sarcoma occurs in about 1–2 per 1,000,000 people a year.[4] They occur most commonly in the third decade of life, with males being affected more often than females (ratio around 1.2:1).[4][2]
Synovial sarcoma usually presents with an otherwise asymptomatic swelling or mass, although general symptoms related to malignancies can be reported such as fatigue.[5]
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 isepithelial 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[3] state that, extremely rarely, there can be a monophasic epithelial form which causes difficulty in differential diagnosis. Depending on the site, there is similarity tobiphenotypic sinonasal sarcoma, although the genetic findings are distinctive.
Like othersoft tissue sarcomas, there is no universalgrading system for reporting histopathology results.[7] In Europe, the Trojani or French system is gaining in popularity[8] while theNCI 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.[7] 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.[9][10]Cytokeratin is typically expressed, at least focally.TLE1,BCL2 andCD99 may be positive but lack specificity.
Most, and perhaps all, cases of synovial sarcoma are associated with a reciprocaltranslocation t(x;18)(p11.2;q11.2). There is some debate about whether the molecular observation itself is definitive of synovial sarcoma.[11][12][13]
The diagnosis of synovial sarcoma is typically made based onhistology and is confirmed by the presence of t(X;18).[6] This translocation event between theSS18 gene on chromosome 18 and one of 3SSX genes (SSX1,SSX2 andSSX4) on chromosome X causes the presence of an SS18-SSXfusion 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.[14] SS18-SSX is thought to underlie synovial sarcoma pathogenesis through dysregulation of gene expression.[3]
There is some association between the SS18-SSX1 or SS18-SSX2 fusion type and both tumour morphology and five-year survival.[15]
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.[17]
Conventionalchemotherapy, (for example,doxorubicin hydrochloride andifosfamide), to reduce the number of remaining microscopicmetastases.[16] The benefit of chemotherapy in synovial sarcoma tooverall survival remains unclear, although a recent study has shown that survival of patients with advanced, poorly differentiated disease marginally improves with doxorubicin/ifosfamide treatment.[16][18]
Radiotherapy to reduce the chance of local recurrence.[16] The benefit of radiotherapy in this disease is less clear than for chemotherapy.[16]
^楊照彬 (2010). "青少年骨髓性肉瘤初期以背痛呈現: 病例報告".台灣復健醫學雜誌 (in Chinese).38 (4):269–275.
^abCoindre, Jean-Michel; Pelmus, Manuela; Hostein, Isabelle; Lussan, Catherine; Bui, Binh N.; Guillou, Louis (2003). "Should molecular testing be required for diagnosing synovial sarcoma? A prospective study of 204 cases".Cancer.98 (12):2700–7.doi:10.1002/cncr.11840.PMID14669292.
^Paul, A.S.; Charalambous, C.; Maltby, B.; Whitehouse, R. (April 2003). "The management of soft-tissue sarcomas of the extremities".Current Orthopaedics.17 (2):124–133.doi:10.1054/cuor.2002.0314.ISSN0268-0890.
^Gill, Anthony J.; Zaborowski, Matthew; Vargas, Ana C.; et al. (19 June 2020). "When used together SS18–SSX fusion-specific and SSX C-terminus immunohistochemistry are highly specific and sensitive for the diagnosis of synovial sarcoma and can replace FISH or molecular testing in most cases".Histopathology.77 (4):588–600.doi:10.1111/his.14190.PMID32559341.S2CID219949018.
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