Synovial sarcoma, also known as malignant synovioma, is a rare form of cancer that occurs in the soft tissues of the body. At the UCSF Sarcoma Center, we take a collaborative and multidisciplinary approach to combat these complex cancers. Our dedicated team of sarcoma specialists provide patients with the most precise diagnostic tools, novel surgical and reconstructive techniques, and promising new therapies.

The UCSF Sarcoma Center includes specialists from:

In addition to our superb clinical care, the UCSF Sarcoma Center is the premier Bay Area institution for leading-edge basic and translational sarcoma research. Through our collaborative research, we are pushing the scientific boundaries to develop new therapies to improve outcomes for patients with sarcoma. 

About Synovial 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.

Primary synovial sarcomas are most common in the soft tissue near the large joints of the arm and leg, but has been found in most human tissues and organs, including the brain, prostate, and heart.

Synovial sarcoma occurs most commonly in the younger patients under 30 years of age. While overall comprising about 8% of all soft tissue sarcomas, it accounts for 15-20% of the cases in adolescents and young adults.

Synovial sarcoma may be classified in different subtypes depending on now it appears under the microscope or the specific gene mutation involved. Synovial sarcoma is a high grade (aggressive) tumor and metastasizes (spreads) to distant sites from the primary tumor in up to 50% of cases.


There are no well-established risk factors for synovial sarcoma. There appears to be a genetic component to the disease, which is associated with the chromosomal translocation t(X;18) (p11;q11). This means that in synovial sarcoma tumor cells parts of chromosome 18 and chromosome X have switched places. It is not unknown whether this mutation occurs sporadically (randomly) or follows a specific chain of events. Because of this translocation, synovial sarcoma cells harbor a mutant gene, which thought to contribute to its development.


Synovial sarcoma usually presents with an otherwise asymptomatic swelling or mass, although general symptoms may be reported such as fatigue. Symptoms vary based on tumor location:

  •  In the head and neck region, it may cause difficulties swallowing and breathing or may alter the voice.
  • The mass may be painful, in particular if nerves are involved.

A slow-growing painless mass is common and may give the false impression that it is harmless. When  deep-seated within the body, it may go undetected. After treatment, surveillance includes regular imaging such as CT scans to detect recurrences at either the area of the original tumor or distant sites in the body (metastatic disease) such as the lungs, which are the most common site for synovial sarcoma metastases. Less than 10% of patients have detectable metastases at the time of initial diagnosis. 


Imaging Studies

One or more of the following may be performed:

  • X-ray
  • Ultrasonography (sonogram)
  • CT scan
  • MRI
  • PET or PET/CT scans of the whole body to look for metastases


A biopsy (removing a sample of the tumor) is done to further characterize the tumor. Among the different types of biopsies:

  • Open biopsy through a surgical incision
  • Core needle biopsy using a large needle (The use of a fine needle to remove cells can establish the cancer, but often do not provide enough tissue to best characterize the tumor)

A pathologist commonly use immunohistochemistry to learn about the tumor cells. Using this technique, the sample tissue is stained with different dyes. How the tumor cells react to the dyes provides additional information about the tumor. Cytopathology, which diagnoses malignant cells on the microscopic or cellular level, is often used to detect the chromosomal translocation specific to synovial sarcoma, which aids in the diagnosis.


A treatment plan is formulated based on the stage (severity) of the disease. The following factors are used to determine pathological stage:

  • Tumor Size
  • Local Invasiveness
  • Histological Subtype
  • Lymph Node Involvement
  • Presence Of Metastases


The following are used in the treatment of synovial sarcoma:


The mainstay of treatment for synovial sarcoma is surgery. The goal is to remove the the tumor and a safety margin of healthy tissue (clear margins).

Radiotherapy (Radiation)

Sometimes it may be difficult for the surgeon to achieve adequate margins around the tumor while preserving function in that areas of the body. Radiotherapy may also be used, either before or after surgery, to reduce the risk of leaving cancer cells behind.


Chemotherapy, typically Doxorubicin and/or Ifosfamide, are used in the treatment of synovial sarcoma, especially in advanced or metastatic disease. Because synovial sarcoma is rare, there is no consensus among experts on just how much of a role chemotherapy plays in preventing metastases and improving survival.

Targeted Therapy

Experimental therapies such as the EZH2 Inhibitor Tazemetostat are being tested in clinical trials to treat synovial sarcoma.

See: A Phase II, Multicenter Study of the EZH2 Inhibitor Tazemetostat in Adult Subjects With INI1-Negative Tumors or Relapsed/Refractory Synovial Sarcoma, a clinical trial being conducted at UCSF.


Prognosis in synovial sarcoma patients is influenced by several factors:

  • The quality of surgery patients receive
  • The characteristics of the disease (including tumor size, local invasiveness, histological subtype, presence of metastases, and lymph node involvement)
  • Patients with small tumors that can be removed with adequate margins have an excellent prognosis.
  • The risk of developing distant metastases is higher for patients with tumors that are greater than 5 cm.
  • Patients with the poorly differentiated subtype are considered to have a worse prognosis
  • Patients with metastases that cannot be resected (removed) have a poor prognosis.