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Updated: Jun 14 2024

Synovial Sarcoma

Images B - axilla - xray - parsons_moved.jpg B - axilla - MRI - parsons_moved.jpg C - leg -ct - parsons_moved.jpg B - Parsons_moved.png A - pelvis - xray - parsons_moved.jpg
  • Summary
    • Synovial Sarcoma is a malignant, soft tissue sarcoma caused by a t(X;18) chromosomal translocation mutation ( SS18:SSX fusion protein) most commonly found near joints but rarely within the joint.
    • The condition usually presents in patients between 15 and 40 years old with a growing mass in proximity to a joint.
    • Diagnosis is made with a biopsy showing a classic mono/biphasic appearance with atypical spindle cells and epithelial cells. Immunostaining is positive for epithelial membrane antigen and vimentin. 
    • Treatment is usually wide surgical excision with perioperative radiation.
  • Epidemiology
    • Demographics
      • 5-10% of all soft tissue sarcomas
      • most common sarcoma found in adolescent age group
      • affects males and females almost equally (1.2 to 1)
    • More common in the lower limbs
      • most commonly around the knee - popliteal fossa
      • it is the most common sarcoma of the foot
  • Etiology
    • Mechanism
      • mesenchymal soft tissue sarcoma with unknown cellular origin
        • synovial sarcoma is a misnomer due to the tumor's microscopic resemblance to mature synovium
    • Pathophysiology
      • synovial sarcoma typically shows high histologic grade
      • metastasis
        • metastasis may develop in 30-60% of patients
          • like other sarcomas, the lung is most common site of metastasis
          • synovial sarcoma has been shown to have similar rates of lymph node metastasis compared to other soft tissue sarcomas 
            • i.e angiosarcoma, clear cell sarcoma, rhabdomyosarcoma, epithelioid sarcoma
            • can stage with lymph node biopsy - called sentinel lymph node biopsy
              • while lymph node metastasis is a poor prognostic sign, it is not as bad as lung metastasis
        • metastasis is more common with large, deep, and high grade sarcomas
    • Genetics
      • chromosomal translocation t(X;18) is observed in more than 90% of cases
      • translocation forms the SYT-SSX1, 2, or 4 fusion protein
        • SYT-SSX4 is rare
      • fusion proteins bind to BAF complex, which displaces the tumor suppressor BAF47
        • new BAF complex activates Sox2, which leads to tumor formation
      • SYT-SSX1 vs. SYT-SSX2
      • SYT-SSX1
      • SYT-SSX2
      • Frequency
      • More common (60% of tumors)
      • Less common (40% of tumors)
      • Histology type
      • Biphasic (contains both spindle cells and epithelial cells)
      • Monophasic (contains either spindle cells OR epithelial cells)
      • Gender
      • M:F = 1:1
      • M:F = 1:2
      • Presentation
      • Larger, with metastases
      • Smaller, without metastases
      • Survival
      • Worse
      • Better
  • Presentation
    • Symptoms
      • typically present as a slow growing mass in proximity to a joint
      • may be painless or painful
      • most commonly occur in periarticular locations
        • knee, shoulder, elbow, foot
        • 60% are found in the lower extremity
    • Physical exam
      • check for regional lymphadenopathy
  • Imaging
    • Ultrasound
      • nonspecific heterogenous hypoechoic mass
    • Radiographs
      • can show soft tissue mineralization (calcification) in these tumors
      • may resemble heterotopic ossification
    • CT
      • Well circumscribed mass
      • can show calcification in the soft tissue mass
      • CT chest for staging
    • MRI
      • Gold standard for diagnostic imaging
      • MRI reveals a heterogenous mass that is typically dark on T1 weighted images and bright on T2 weighted images
      • T2 "triple sign"
        • areas of high signaling form necrosis/cystic degeneration and low signaling from calcifications and fibrosis
    • Staging
      • Biopsy
        • core-needle versus incisional biopsy
        • FNA is not gold-standard as it does not provide information on tumor structure
      • CT Chest
      • PET/CT Scan
  • Histology
    • Characteristic findings
      • classical synovial sarcoma shows a mono/biphasic appearance with two typical cell types
        • spindle cell type is most common
          • relatively small and uniform and found in sheets of malignant appearing cells with minimal cytoplasm and dark atypical nuclei
        • epithelial cell type
          • gland, nest, or cyst-like cells
      • cellular origin of synovial sarcoma is unknown
    • Immunostaining
    • synovial sarcoma stains positive for
      • vimentin
      • epithelial membrane antigen
      • sporadic S-100
      • epithelial cells stain positive for keratin
  • Treatment
    • Operative
      • wide surgical resection with perioperative radiotherapy
        • indications
          • standard of care in most patients
        • technique
          • radiotherapy
            • may be delivered in neoadjuvant or adjuvant fashion
              • no consensus as to which provides better outcomes
            • decreases the rate of local recurrence and improves overall survival and disease-specific survival
          • chemotherapy
            • data regarding chemotherapy in synovial sarcoma suggests that chemotherapy may improve both local control and overall survival
            • routine use is limited and there is no consensus for regimen or timing of chemotherapy
            • Reserved for high risk tumors, metastatic disease, and younger populations
  • Prognosis
    • Overall prognosis is poor
      • 5 year survival is approximately 50-60%
      • 10 year survival is approximately 25%
      • Prognostic factors include size, grade, location, patient age, and surgical margins
    • SYT-SSX fusion type is most important prognostic factor 
      • SYT-SSX2 better survival
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