Synonyms

• Soft tissue osteosarcoma
• extraosseous osteosarcoma

Category

Soft tissue

Behaviour

Malignant

Grade

High

Gender

Both equally

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

• 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)
• Years 2–3: 3-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 2 - MUGA or ECHO
• Year 4: 6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 4 - MUGA or ECHO
• Year 5: 6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry
• Years 6–10: Annual clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 6 - MUGA or ECHO
• Discharge at 10 years after surgery