Synovial sarcoma
Encyclopedia
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 sarcoma
s.
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.
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 but about 15-20% of cases in adolescents and young adults. The peak of incidence is before the 30th birthday and males are affected more often than females (ratio around 1.2:1).
Like other soft tissue sarcoma
s, 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 account of a number of other factors.
t(x;18)(p11.2;q11.2). There is some debate about whether the molecular observation itself is definitional 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 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.
There is some association between the SS18-SSX1 or SS18-SSX2 fusion type and both tumour morphology and five-year survival.
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
which usually occurs near to the joints of the arm, neck or leg. It is one of the soft tissue sarcoma
Soft tissue sarcoma
A soft-tissue sarcoma is a form of sarcoma that develops in connective tissue, though the term is sometimes applied to elements of the soft tissue that are not currently considered connective tissue.-Risk factors:...
s.
Synovial sarcoma was originally coined early in the 20th century as some thought that the microscopic similarity of some tumors to synovium
Synovium
Synovial membrane is the soft tissue found between the articular capsule and the joint cavity of synovial joints....
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.
Primary synovial sarcomas are most common in the soft tissue
Soft tissue
In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...
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 but about 15-20% of cases in adolescents and young adults. The peak of incidence is before the 30th birthday and males are affected more often than females (ratio around 1.2:1).
Histopathology
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 state that, extremely rarely, there can be a monophasic epithelial form which causes difficulty in differential diagnosis.Like other soft tissue sarcoma
Soft tissue sarcoma
A soft-tissue sarcoma is a form of sarcoma that develops in connective tissue, though the term is sometimes applied to elements of the soft tissue that are not currently considered connective tissue.-Risk factors:...
s, there is no universal grading system for reporting histopathology results. In Europe, the Trojani or French system is gaining in popularity while the NCI
NCI
NCI can stand for:*National Cancer Institute*National Captioning Institute*Nordic Centre in India*National College of Ireland*Native Communications Inc - Aboriginal Public Broadcaster in Manitoba, Canada....
grading system is more common in the United States. The Trojani system scores the sample, depending on tumour differentiation, mitotic index
Mitotic index
Mitotic index is a measure for the proliferation status of a cell population. It is defined as the ratio between the number of cells in mitosis and the total number of cells....
, 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 account of a number of other factors.
Molecular biology
Most, and perhaps all, cases of synovial sarcoma are associated with a reciprocal translocationChromosomal translocation
In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer. It is detected on...
t(x;18)(p11.2;q11.2). There is some debate about whether the molecular observation itself is definitional 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
SS18
Protein SSXT is a protein that in humans is encoded by the SS18 gene.-Interactions:SS18 has been shown to interact with MLLT10, EP300, SMARCB1 and SMARCA2.-Further reading:...
gene on chromosome 18 and one of 3 SSX
Synovial sarcoma, X breakpoint
Synovial sarcoma, X breakpoint refers to a group of genes associated with synovial sarcoma.They include:* SSX1* SSX2 and SSX2B* SSX3* SSX4 and SSX4B* SSX5* SSX6* SSX7* SSX8* SSX9* SSX10...
genes (SSX1
SSX1
Protein SSX1 is a protein that in humans is encoded by the SSX1 gene.-Further reading:...
, SSX2
SSX2
Protein SSX2 is a protein that in humans is encoded by the SSX2 gene.-Further reading:...
and SSX4
SSX4 (gene)
Protein SSX4 is a protein that in humans is encoded by the SSX4 gene.-Further reading:...
) 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.
There is some association between the SS18-SSX1 or SS18-SSX2 fusion type and both tumour morphology and five-year survival.
Symptoms
Synovial sarcoma usually presents with an otherwise asymptomatic swelling or mass, although general symptoms related to maligancies can be reported such as fatigue.Treatment
Treatment usually involves:- SurgerySurgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
, 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 chemotherapyChemotherapyChemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
, (for example, doxorubicin hydrochloride and ifosfamideIfosfamideIfosfamide is a nitrogen mustard alkylating agent used in the treatment of cancer.It is sometimes abbreviated "IFO".-Uses:It is given as a treatment for a variety of cancers, including:...
), to reduce the number of remaining microscopic cancer cells. The benefit of chemotherapy in synovial sarcoma to overall survival remains unclear, although a recent study has shown that survival of patients with advanced, poorly differentiated disease marginally improves with doxorubicin/ifosfamide treatment. - Radiotherapy to reduce the chance of local recurrence. The benefit of radiotherapy in this disease is less clear than for chemotherapy.
External links
- Ferrari and Collini Synovial Sarcoma ESUN (December 15, 2005)
- humpath #1965 (Pathology images)