Surgical Pathology Criteria

Synovial Sarcoma

Differential Diagnosis

Biphasic synovial sarcoma

Monophasic synovial sarcoma, spindled

Synovial sarcoma with poorly differentiated areas

Malignant Peripheral Nerve Sheath Tumor, Glandular Biphasic Synovial Sarcoma
Spindle cells may be larger and pleomorphic Spindle cells small and bland
Frequently involves nerve or neurofibroma Rarely involves nerve
Frequently associated with von Recklinghausen No association
No ropy collagen Ropy collagen frequent
Calcification infrequent Calcification frequent
No hemangiopericytomatous vessels Hemangiopericytomatous vessels frequent
No SYT-SSX gene fusion SYT-SST gene fusion present
TLE1 5% TLE1 97%

 

Carcinoma Biphasic Synovial Sarcoma
Spindle cell component rare (carcinosarcoma, metaplastic carcinoma) Virtually always a spindle cell component
Usually older patient Usually teenagers or young adults
May be pleomorphic No more than mild pleomorphism
No SYT-SSX gene fusion SYT-SST gene fusion present
TLE1 14% (carcinosarcoma) TLE1 97%

 

Diffuse Type Tenosynovial Giant Cell Tumor Biphasic Synovial Sarcoma
No epithelial lining of spaces May have epithelial lined glands
Keratin negative Keratin positive
Usually involves joint Very rarely involves joint
Giant cells may be frequent Giant cells infrequent
No ropy collagen Ropy collagen frequent
Nuclei frequently round, some are grooved Nuclei elongated in spindle component
No SYT-SSX gene fusion SYT-SST gene fusion present

 

Adult Fibrosarcoma Monophasic Synovial Sarcoma
Usually extensive herringbone pattern Herringbone pattern usually only focal
Keratin, EMA negative Keratin, EMA often positive
No ropy collagen Ropy collagen frequent
Calcification rare Calcification may be present
No hemangiopericytomatous vessels Hemangiopericytomatous vessels frequent
Thin elongate nuclei Plump nuclei
Chromatin not stippled Stippled chromatin
No SYT-SSX gene fusion SYT-SST gene fusion present
TLE1 0% (0/3) TLE1 97%

 

Leiomyosarcoma Monophasic Synovial Sarcoma
Cells usually larger and pleomorphic Cells small and bland
Spindled cytoplasm Scant cytoplasm
Actin positive Actin negative
No ropy collagen Ropy collagen frequent
Calcification infrequent Calcification frequent
No hemangiopericytomatous vessels Hemangiopericytomatous vessels frequent
Chromatin not stippled Stippled chromatin
No SYT-SSX gene fusion SYT-SST gene fusion present
TLE1 2% TLE1 97%

 

Both may present as keratin positive spindle cell neoplasms
Epithelioid Sarcoma Monophasic Synovial Sarcoma
Usually superficial Usually deep
Necrosis frequently extensive Necrosis usually focal
CD34 50% positive CD34 negative
No ropy collagen Ropy collagen frequent
Calcification infrequent Calcification frequent
No hemangiopericytomatous vessels Hemangiopericytomatous vessels frequent
No SYT-SSX gene fusion SYT-SST gene fusion present
TLE1 0% (0/2) TLE1 97%
CA125 90% positive CA125 negative

 

Synovial Sarcoma Clear Cell Sarcoma
Dense nuclei with stippled chromatin Vesicular nuclei with prominent nucleoli
Keratin 50-80% positive Keratin negative (one report of 30% positive)
Melanin and HMB45 negative Melanin and HMB45 positive 80%
Calcification common Calcification uncommon
SYT-SSX gene fusion present t(11;12) frequent
TLE1 97% TLE1 14%

 

Palmar or Plantar Fibromatosis Synovial Sarcoma
Rare under age 20 Frequently under age 20
Multiple small nodules Single large mass
Not biphasic May be biphasic
Variable cellularity Uniformly hypercellular
Lacks ropy collagen, calcification and stag horn vessels May have ropy collagen, calcification and stag horn vessels
No SYT-SSX fusion SYT-SSX fusion present

 

Poorly differentiated areas of synovial sarcoma and some monophasic cases may be difficult to impossible to distinguish from tumors such as:

  • Malignant peripheral nerve sheath tumor
  • Fibrosarcoma
  • Hemangiopericytoma
  • Primitive peripheral neuroectodermal tumor
  • Focally poorly differentiated cases are distinguished by identification of typical areas
  • Pure poorly differentiated cases may require cytogenetic confirmation
  • FISH is indicated in such cases

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