SYNOVIAL SARCOMA
Malignant Soft Tissue Sarcoma | t(X;18) SYT-SSX Translocation | Young Adults Near Joints
Histological Classification
Critical Must-Knows
- Third most common soft tissue sarcoma in young adults (after liposarcoma and MFH)
- t(X;18) translocation creating SYT-SSX fusion is pathognomonic (present in over 95%)
- Name is misleading - does NOT arise from synovium but occurs near joints in 60-70%
- Calcification present in 30% on imaging - rare for soft tissue sarcomas
- Wide excision plus adjuvant chemotherapy and radiation is standard multimodal treatment
Examiner's Pearls
- "SYT-SSX1 fusion (biphasic type) has worse prognosis than SYT-SSX2 fusion (monophasic)
- "Despite name, synovial sarcoma does NOT arise from joint synovium
- "Lung is most common metastatic site (90%), bone metastases in 10-20%
- "Poorly differentiated subtype has 5-year survival under 20% versus 60% for well-differentiated
Clinical Imaging
Imaging Gallery
Critical Synovial Sarcoma Exam Points
Molecular Diagnosis
t(X;18) translocation creating SYT-SSX fusion is pathognomonic - Present in over 95% of synovial sarcomas. RT-PCR or FISH testing confirms diagnosis. SYT-SSX1 fusion has worse prognosis than SYT-SSX2.
Multimodal Treatment
Wide excision plus chemotherapy and radiation - Unlike many soft tissue sarcomas, synovial sarcoma is chemosensitive. Ifosfamide-based chemotherapy improves survival, especially in high-risk patients.
Misleading Name
Does NOT arise from joint synovium - Despite the name, synovial sarcoma arises from pluripotent mesenchymal cells, not synovial lining. Occurs near joints in 60-70% but can occur anywhere.
Calcification on Imaging
Calcification in 30% of cases - Unusual for soft tissue sarcomas but characteristic of synovial sarcoma. Appears as stippled or curvilinear calcification on X-ray and CT.
SYNOVIALSynovial Sarcoma Key Features
Memory Hook:SYNOVIAL reminds you of all key features - from SYT-SSX fusion to Lung metastases!
BMPSynovial Sarcoma Histological Subtypes
Memory Hook:BMP - Biphasic is Most Poor prognosis (SYT-SSX1 worse than SSX2)!
PLANSPoor Prognostic Factors in Synovial Sarcoma
Memory Hook:Poor PLANS lead to poor outcomes in synovial sarcoma!
Overview and Epidemiology
Synovial sarcoma is a malignant soft tissue tumor characterized by the pathognomonic t(X;18) chromosomal translocation. Despite its name, synovial sarcoma does NOT arise from joint synovium but from pluripotent mesenchymal cells. It is the third most common soft tissue sarcoma in young adults (after liposarcoma and malignant fibrous histiocytoma), accounting for 5-10% of all soft tissue sarcomas.
Misleading Nomenclature
The name "synovial sarcoma" is historically based but anatomically incorrect. The tumor was named in the early 20th century due to its microscopic resemblance to synovial tissue and frequent occurrence near joints. However, modern molecular studies confirm it arises from primitive mesenchymal cells, NOT from joint synovium. Up to 30% occur away from joints entirely.
Demographics
- Age: Peak 15-35 years (adolescents and young adults)
- Gender: Equal male and female distribution
- Pediatric: 15-20% occur in children under 15 years
- Rare in elderly: Uncommon over 50 years
Location Distribution
- Lower extremity: 60-70% (knee, ankle, foot most common)
- Upper extremity: 15-20% (hand, wrist, forearm)
- Trunk: 10-15%
- Head/neck: 5-10% (rare but reported)
Specific Anatomical Sites
| Anatomical Region | Frequency | Typical Presentation | Prognostic Consideration |
|---|---|---|---|
| Knee/thigh | 30-40% | Deep-seated mass near joint | Standard prognosis, limb salvage usually feasible |
| Foot/ankle | 20-30% | Superficial or deep mass, often calcified | Good prognosis, smaller tumors at presentation |
| Hand/forearm | 10-15% | Slow-growing mass, may mimic ganglion | Good prognosis, smaller size |
| Trunk/abdominal wall | 10-15% | Large at diagnosis, deep location | Worse prognosis, difficult margins |
| Head/neck | 5-10% | Rare, complex anatomy | Worse prognosis, margin challenges |
Pathophysiology and Molecular Biology
Cellular Origin and Genetics
Synovial sarcoma arises from pluripotent mesenchymal stem cells with the capacity for epithelial differentiation. The pathognomonic t(X;18) translocation drives oncogenesis.
t(X;18) Translocation
Pathognomonic molecular hallmark present in over 95% of synovial sarcomas:
- Translocation between chromosome X (SYT gene) and chromosome 18 (SSX1 or SSX2 gene)
- Creates SYT-SSX fusion protein
- Functions as aberrant transcription factor
- Disrupts chromatin remodeling and gene expression
Fusion Variants
Two main fusion types with prognostic significance:
- SYT-SSX1 (65%): Associated with biphasic histology, worse prognosis
- SYT-SSX2 (35%): Associated with monophasic histology, better prognosis
- Rare variants: SYT-SSX4 (under 1%), similar prognosis to SSX2
Molecular Testing is Diagnostic
RT-PCR or FISH for t(X;18) is essential for confirming diagnosis. The presence of SYT-SSX fusion is pathognomonic for synovial sarcoma. Fusion type (SSX1 vs SSX2) has prognostic significance - SSX1 associated with worse outcomes. All suspected synovial sarcomas should undergo molecular testing.
Tumor Biology and Growth Pattern
| Characteristic | Description | Clinical Implication |
|---|---|---|
| Growth pattern | Slow-growing initially, then rapid progression | Long symptom duration (months to years) before diagnosis |
| Local invasion | Infiltrative along fascial planes and neurovascular bundles | Wide margins essential, neurovascular sacrifice may be needed |
| Metastatic potential | High - 40-50% metastasize within 5 years | Lung metastases in 90%, bone in 10-20% |
| Calcification | Present in 30% (rare for soft tissue sarcomas) | Diagnostic clue on imaging |
Classification and Histology
WHO Histological Classification
Biphasic Synovial Sarcoma (20-30%)
Classic appearance with both epithelial and spindle cell components clearly visible.
Histological Features
- Epithelial component: Gland-like structures, columnar or cuboidal cells
- Spindle cell component: Monotonous spindle cells in fascicles
- Two components intimately admixed
- Clear distinction between both components
Molecular and Prognosis
- SYT-SSX1 fusion most common (over 90%)
- Worse prognosis than monophasic type
- 5-year survival: 40-50%
- Higher metastatic rate: 50-60%
The biphasic pattern is diagnostic when both components are prominent, making diagnosis easier.
Immunohistochemistry
| Marker | Positive Rate | Diagnostic Value |
|---|---|---|
| EMA (epithelial membrane antigen) | 70-100% | Supportive but not specific |
| Cytokeratin (AE1/AE3) | 60-90% | Supportive but not specific |
| TLE1 (nuclear) | 90-95% | Sensitive marker, helps distinguish from other sarcomas |
| BCL2 | 90% | Supportive but non-specific |
| CD99 | 60-70% | May cause confusion with Ewing sarcoma |
TLE1 nuclear staining is the most sensitive immunohistochemical marker, but molecular confirmation remains gold standard.
Clinical Presentation
History
Presenting Symptoms
- Painless mass: Most common (60-70%)
- Painful mass: 30-40% (larger tumors, neurovascular involvement)
- Slow growth: Months to years before diagnosis
- Joint symptoms: Pain, stiffness if near joint (30%)
Duration of Symptoms
- Average: 2-4 years before diagnosis
- Long latency: Misdiagnosed as benign (ganglion, lipoma)
- Rapid growth: Suggests high-grade or poorly differentiated
- Delay common: Slow growth leads to diagnostic delay
Diagnostic Delay is Common
Average time from symptom onset to diagnosis is 2-4 years. Synovial sarcoma is frequently misdiagnosed as benign lesion (ganglion cyst, lipoma, tendon sheath tumor) due to slow growth and location near joints. Any persistent soft tissue mass in a young adult should undergo imaging and biopsy.
Physical Examination
Examination Approach
Observe:
- Size of mass (median 5cm at diagnosis)
- Location relative to joint
- Skin changes (rare except for superficial lesions)
- Venous engorgement (large tumors)
Assess:
- Consistency (firm to hard, unlike soft lipomas)
- Mobility (deep lesions often fixed to fascia)
- Tenderness (30-40% tender on palpation)
- Relation to neurovascular structures
Document:
- Range of motion of adjacent joint
- Neurovascular status distal to mass
- Muscle strength and function
- Signs of nerve compression or vascular compromise
Check:
- Lymph nodes (nodal metastases rare but possible in 5%)
- Chest examination (lung metastases uncommon at presentation)
Complete examination provides baseline for treatment planning.
Investigations and Imaging
Imaging Protocol
Plain X-rays
Initial imaging - essential for all soft tissue masses.
Key findings:
- Calcification: Present in 30% - stippled or curvilinear pattern
- Bone erosion: Adjacent bone erosion if large and juxta-osseous
- Soft tissue mass: Visible if large enough
- Periosteal reaction: Rare, indicates bone involvement
Calcification is Diagnostic Clue
Calcification in a soft tissue mass is rare for sarcomas (occurs in under 10% overall) but is present in 30% of synovial sarcomas. This is a diagnostic clue that should raise suspicion for synovial sarcoma in young adults with soft tissue mass near a joint.
Plain radiographs are screening only - MRI is required for definitive local staging.
Biopsy
Biopsy Principles for Synovial Sarcoma
Critical rules:
- Core needle biopsy (14-16 gauge) preferred - minimally invasive
- Biopsy tract must be excisable at definitive surgery (longitudinal approach)
- Request molecular testing - RT-PCR or FISH for t(X;18) translocation
- Adequate tissue - multiple cores for histology and molecular studies
- Referral to sarcoma center before biopsy is ideal
Never perform excisional biopsy for suspected sarcoma - risks inadequate margins and tumor seeding.
Staging System
AJCC 8th Edition Staging (Soft Tissue Sarcoma)
| Stage | Grade | Size/Depth | 5-Year Survival |
|---|---|---|---|
| IA | Low (G1) | Superficial or deep, any size | 90% |
| IB | Low (G1) | Deep, greater than 5cm | 80% |
| II | Low (G1) | Deep, greater than 10cm OR High (G2-3) under 5cm | 70% |
| IIIA | High (G2-3) | Superficial/deep, 5-10cm | 60% |
| IIIB | High (G2-3) | Deep, greater than 10cm | 40-50% |
| IV | Any | Metastatic disease (M1) | 10-20% |
Most synovial sarcomas are intermediate to high grade (G2-G3) by virtue of their biology.
Management
Core Principles
Multimodal Treatment is Standard
Synovial sarcoma requires multimodal treatment: Wide surgical resection PLUS adjuvant chemotherapy PLUS radiation therapy. Unlike many soft tissue sarcomas, synovial sarcoma is chemosensitive. Ifosfamide-based chemotherapy improves survival, particularly for high-risk patients (larger than 5cm, high grade, deep location).
Treatment Fundamentals:
- Surgery: Wide excision with 2cm margins is the goal
- Chemotherapy: Ifosfamide-based regimens (chemosensitive tumor)
- Radiation: 50-66 Gy pre- or postoperative
These principles apply to all synovial sarcoma cases.
Surgical Technique
Preoperative Planning
Preparation Steps
- Review MRI with radiology and surgical team
- Identify tumor extent, neurovascular involvement
- Plan resection margins (2cm goal for synovial sarcoma)
- Assess need for vascular or nerve reconstruction
- Mark biopsy tract for en bloc excision
- Plan incision to incorporate biopsy site
- Avoid transverse incisions (limit extensile approaches)
- Consider drain sites as contaminated
- Anticipate defect size and depth
- Arrange soft tissue coverage (flap, graft)
- Plan tendon transfers if muscle resection needed
- Vascular surgery backup if vessel reconstruction needed
Preparation ensures optimal surgical outcome.
Complications
Treatment-Related Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Local recurrence | 15-30% at 5 years | Positive margins, large size, high grade | Re-resection if feasible, amputation for failed limb salvage |
| Distant metastases | 40-50% at 5 years | High grade, larger than 5cm, poorly differentiated | Systemic chemotherapy, metastasectomy if oligometastatic |
| Wound complications | 15-30% (higher with preop RT) | Preoperative radiation, poor soft tissue coverage | Wound care, VAC therapy, flap coverage if needed |
| Nerve injury | 10-20% | Neurovascular proximity, intentional sacrifice | Physiotherapy, orthotics, nerve reconstruction if feasible |
| Radiation fibrosis | 20-40% at 10 years | High radiation dose, large field | Physiotherapy, stretching, manage expectations |
| Chemotherapy toxicity | 50-80% (varies by regimen) | High-dose ifosfamide, doxorubicin cumulative dose | Supportive care, growth factors, dose modification |
Postoperative Care and Surveillance
Recovery Protocol
Postoperative Management
Inpatient care:
- Wound monitoring (flap viability, hematoma, infection)
- DVT prophylaxis (LMWH)
- Pain management (multimodal analgesia)
- Drain management (remove when under 30ml per 24 hours)
Clinic review:
- Wound healing assessment
- Suture removal at 2-3 weeks
- Final pathology review (margins, grade, molecular)
- Plan adjuvant therapy (chemotherapy and/or radiation)
Chemotherapy and radiation:
- Chemotherapy cycles (4-6 cycles over 3-4 months)
- Radiotherapy (5-7 weeks, 50-66 Gy)
- Monitor for treatment toxicity
- Maintain physiotherapy during treatment
Follow-up schedule:
- Years 1-2: Every 3 months
- Years 3-5: Every 6 months
- Beyond 5 years: Annually
Imaging and surveillance detailed below.
Surveillance Protocol
Years 1-2 (High Risk)
Every 3 months:
- Clinical examination
- Chest CT (detect lung metastases early)
- MRI primary site every 6 months
- 70% of recurrences occur in first 3 years
Years 3-5
Every 6 months:
- Clinical examination
- Chest CT every 6 months
- MRI primary site annually
- Late recurrences possible
Beyond 5 Years
Annually:
- Clinical examination
- Chest imaging (X-ray or CT)
- Local imaging if symptoms
- Late metastases can occur 10+ years
Metastatic Surveillance
High metastatic rate requires vigilant imaging:
- Lung CT: High-resolution for nodule detection
- PET-CT: If recurrence suspected, assess resectability
- Bone scan: If bone pain (10-20% bone metastases)
Prognosis and Outcomes
Prognostic Factors
| Factor | Favorable | Unfavorable |
|---|---|---|
| Histology | Monophasic, SYT-SSX2 | Poorly differentiated, SYT-SSX1 |
| Size | Under 5cm | Greater than 5cm |
| Depth | Superficial | Deep (subfascial) |
| Age | Under 25 years | Over 25 years |
| Margin status | Negative (greater than 2mm) | Positive |
| Fusion type | SYT-SSX2 | SYT-SSX1 |
| Chemotherapy response | Greater than 90% necrosis | Poor response |
Survival by Subtype and Stage
5-Year Survival Rates
| Category | 5-Year Survival | 10-Year Survival |
|---|---|---|
| Overall (all stages) | 50-60% | 35-45% |
| Localized, under 5cm | 70-80% | 55-65% |
| Localized, greater than 5cm | 50-60% | 35-45% |
| Poorly differentiated subtype | Under 20% | Under 10% |
| Metastatic at presentation | 10-20% | Under 10% |
Fusion Type is Prognostic
SYT-SSX fusion type has prognostic significance: SYT-SSX1 fusion (associated with biphasic histology) has worse prognosis (5-year survival 40-50%) compared to SYT-SSX2 fusion (associated with monophasic histology, 5-year survival 60-70%). This is independent of other factors.
Evidence Base and Key Studies
t(X;18) Translocation in Synovial Sarcoma
- Identified t(X;18) translocation as pathognomonic for synovial sarcoma
- SYT-SSX fusion gene created by translocation drives oncogenesis
- Present in over 95% of synovial sarcomas
- Established molecular diagnosis as gold standard
SYT-SSX Fusion Type and Prognosis
- SYT-SSX1 fusion associated with worse prognosis than SYT-SSX2
- SYT-SSX1: 5-year survival 45% vs SYT-SSX2: 70%
- SYT-SSX1 more common in biphasic histology (90% vs 10%)
- Fusion type independent prognostic factor
Chemotherapy in High-Risk Synovial Sarcoma
- Randomized trial of surgery plus radiotherapy vs surgery plus radiotherapy plus chemotherapy
- Chemotherapy improved 5-year survival: 65% vs 50%
- Benefit greater for high-risk patients (greater than 5cm, deep, high grade)
- Ifosfamide-based regimens most effective
Long-Term Outcomes and Metastatic Pattern
- 271 patients with synovial sarcoma, median follow-up 7 years
- 5-year survival: 56%, 10-year survival: 42%
- Metastatic rate: 45% at 10 years (lungs 90%, bone 10%)
- Positive margins increased recurrence from 10% to 40%
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Adult with Ankle Mass - Diagnosis and Workup
"A 22-year-old woman presents with a 4cm painless mass on the medial aspect of her ankle, present for 18 months and slowly enlarging. MRI shows a multiloculated soft tissue mass with triple sign on T2 imaging and small areas of calcification on X-ray. What is your differential diagnosis and management approach?"
Scenario 2: Treatment Planning for High-Risk Synovial Sarcoma
"A 28-year-old man has biopsy-proven synovial sarcoma of the thigh (8cm, deep to fascia, SYT-SSX1 fusion, biphasic histology). CT chest shows no metastases. The tumor is adjacent to the femoral neurovascular bundle. How would you manage this case?"
Scenario 3: Metastatic Synovial Sarcoma Management
"A 30-year-old woman treated 2 years ago for synovial sarcoma of the foot (wide excision, chemotherapy, radiation) now presents with 3 lung nodules on surveillance CT (largest 2cm, all in right lung). PET-CT shows FDG-avid nodules, no other disease. How do you proceed?"
MCQ Practice Points
Molecular Biology Question
Q: What chromosomal translocation is pathognomonic for synovial sarcoma? A: t(X;18) translocation creating SYT-SSX fusion - Present in over 95% of synovial sarcomas. The translocation fuses the SYT gene on chromosome X with either SSX1 or SSX2 gene on chromosome 18. SYT-SSX1 fusion has worse prognosis than SYT-SSX2. RT-PCR or FISH confirms diagnosis.
Epidemiology Question
Q: What is the peak age and most common location for synovial sarcoma? A: Peak age 15-35 years (young adults), most common near large joints (knee, ankle, foot) in 60-70%. Despite the name, synovial sarcoma does NOT arise from joint synovium but from mesenchymal cells. It is the third most common soft tissue sarcoma in young adults.
Imaging Question
Q: What imaging finding is characteristic of synovial sarcoma but rare for other soft tissue sarcomas? A: Calcification - present in 30% of synovial sarcomas but rare (under 10%) in most other soft tissue sarcomas. Appears as stippled or curvilinear calcification on X-ray and CT. MRI triple sign (three signal intensities on T2) is also characteristic.
Treatment Question
Q: How does treatment of synovial sarcoma differ from most other soft tissue sarcomas? A: Synovial sarcoma is chemosensitive and requires multimodal treatment: surgery PLUS chemotherapy PLUS radiation. Ifosfamide-based chemotherapy improves survival in high-risk patients. Response rate is 30-50%, better than most soft tissue sarcomas. Wide excision alone is insufficient.
Prognosis Question
Q: What is the 5-year survival for synovial sarcoma and what is the most common site of metastasis? A: Overall 5-year survival is 50-60%. Lungs are the most common metastatic site (90% of metastases). Metastatic rate is 40-50% at 5 years. Poor prognostic factors include: size greater than 5cm, poorly differentiated histology, SYT-SSX1 fusion, positive margins.
Australian Context
Sarcoma Service Referral
Australian sarcoma centers:
- Peter MacCallum Cancer Centre (VIC)
- Royal Prince Alfred Hospital (NSW)
- Princess Alexandra Hospital (QLD)
- Royal Perth Hospital (WA)
Referral indication: Any suspected soft tissue sarcoma should be referred BEFORE biopsy.
Medicare and PBS
Funding considerations:
- MRI and CT staging: Medicare rebateable
- Molecular testing (t(X;18)): Available at sarcoma centers
- Chemotherapy: PBS-listed (doxorubicin, ifosfamide)
- Radiotherapy: Public hospital access
Medicolegal Considerations
Key documentation requirements:
- Diagnostic delay: Document investigation pathway for persistent soft tissue masses
- Pre-biopsy staging completed and documented
- Molecular testing requested on biopsy
- MDT discussion before definitive treatment
- Informed consent including multimodal treatment, recurrence risk, metastatic potential
- Surveillance plan documented at discharge
Common litigation issues:
- Delayed diagnosis (misdiagnosed as benign ganglion or lipoma for years)
- Inadequate staging before surgery
- Failure to obtain molecular confirmation
- Surgery without adjuvant therapy in high-risk cases
- Inadequate surveillance leading to late detection of metastases
SYNOVIAL SARCOMA
High-Yield Exam Summary
Key Epidemiology
- •Third most common soft tissue sarcoma in young adults (5-10% of all soft tissue sarcomas)
- •Peak age 15-35 years, equal male and female distribution
- •60-70% near large joints (knee, ankle, foot), but does NOT arise from synovium
- •Misleading name - arises from mesenchymal cells not synovial tissue
Molecular Biology (Pathognomonic)
- •t(X;18) translocation creating SYT-SSX fusion present in over 95%
- •SYT-SSX1 fusion (65%): Biphasic histology, worse prognosis (5-year survival 40-50%)
- •SYT-SSX2 fusion (35%): Monophasic histology, better prognosis (5-year survival 60-70%)
- •RT-PCR or FISH confirms diagnosis - molecular testing essential
Histological Classification
- •Biphasic (20-30%): Epithelial AND spindle components visible
- •Monophasic (60-70%): Spindle cells only, epithelial component hidden
- •Poorly differentiated (10-15%): High-grade, under 20% 5-year survival
- •Immunohistochemistry: TLE1 (90-95% sensitive), EMA, cytokeratin positive
Clinical Presentation and Imaging
- •Painless slow-growing mass (60-70%), average 2-4 years symptom duration
- •Calcification in 30% on imaging - rare for soft tissue sarcomas (diagnostic clue)
- •MRI triple sign: Three signal intensities on T2 (characteristic)
- •CT chest essential for staging - lungs are site of 90% of metastases
Treatment Principles (Multimodal)
- •Wide excision with 2cm margins (negative margins critical)
- •Chemotherapy: Ifosfamide-based regimens (synovial sarcoma is chemosensitive, response rate 30-50%)
- •Radiotherapy: 50-66 Gy adjuvant for high-risk or close margins
- •Multimodal treatment (surgery plus chemo plus radiation) is standard unlike many sarcomas
- •Neoadjuvant chemotherapy for large (greater than 5cm) or high-risk tumors
Poor Prognostic Factors (PLANS Mnemonic)
- •Poorly differentiated histology (under 20% 5-year survival)
- •Large size (greater than 5cm)
- •Age over 25 years
- •Neurovascular invasion
- •SYT-SSX1 fusion type (worse than SSX2)
Prognosis and Surveillance
- •Overall 5-year survival: 50-60%, 10-year survival: 35-45%
- •Metastatic rate: 40-50% at 5 years (lungs 90%, bone 10-20%)
- •Local recurrence: 15-30% (negative margins essential)
- •Surveillance: Every 3 months years 1-2, every 6 months years 3-5, annually after 5 years
- •Chest CT critical - 70% of metastases occur within first 3 years