Extraskeletal Osteosarcoma
Synonyms: Soft tissue osteosarcoma, extraosseous osteosarcoma
Bone formation in soft tissue is key diagnostic feature
Quick Facts
Behaviour
Malignant
Category
Soft tissue
Grade
High
Synonyms
- Soft tissue osteosarcoma
- extraosseous osteosarcoma
Category
Soft tissue
Behaviour
Malignant
Grade
High
Gender
M = F
Tissue of Origin
Other
Epidemiology
- Rare osteosarcoma arising in soft tissues
- Peak incidence in middle-aged to older adults
- Lower extremity and trunk predominance
Clinical Features
- Rapidly growing mass
- Pain if compressing adjacent structures
- Often large at diagnosis
Location
- Lower extremity (thigh)
- Trunk
- Upper extremity
- Any soft tissue site
Imaging
- MRI: soft tissue mass with areas of ossification
- CT: demonstrates Bone/mineral formation
Pathology
- Malignant mesenchymal cells producing osteoid
- High-grade sarcoma with no Bone origin
- Direct arising from soft tissue
Genetics
- TP53, RB1 mutations reported
- Complex karyotype
Treatment
- Wide surgical excision
- Chemotherapy similar to conventional osteosarcoma
Prognosis
- Poor - High-grade malignancy
- Survival similar to conventional osteosarcoma
Key Points
- Bone formation in soft tissue is key diagnostic feature
- Younger adults than typical soft tissue sarcomas
- Aggressive with metastatic potential
Workup - Blood Tests
- FBC, U&E, LFTs, Bone profile - baseline
- Alkaline phosphatase, LDH
Workup - Local Imaging
MRI with contrast primary site - local staging
Workup - Biopsy
Core needle biopsy - confirm osteosarcoma diagnosis
Workup - Staging
- CT chest/abdomen/pelvis - metastases
- PET-CT
Workup - Other
- MDT at specialist soft tissue sarcoma centre
- Chemotherapy indicated
Follow-up Summary
- 1
Year 1
Post-operative visit within first 6 weeks (if primary surgery); 2-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry (U&E, LFT, Ca, PO4, Mg, HCO3); end of Year 1 - gonadal function (males: testosterone, LH, FSH; females: oestradiol, LH, FSH)
- 2
Years 2–3
3-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 2 - MUGA or ECHO
- 3
Year 4
6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 4 - MUGA or ECHO
- 4
Year 5
6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry
- 5
Years 6–10
Annual clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 6 - MUGA or ECHO
- 6
Discharge at 10 years after surgery
Medical disclaimer
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