Synovial Sarcoma
Differential Diagnosis
Biphasic synovial sarcoma
Monophasic synovial sarcoma, spindled
Synovial sarcoma with poorly differentiated areas
- Malignant peripheral nerve sheath tumor
- Fibrosarcoma
- Hemangiopericytoma
- Primitive peripheral neuroectodermal tumor
| 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
