Osteosarcoma

Classic Osteosarcoma (Intramedullary)

Epidemiology

  • Male-to-female ratio: 1.5:1
  • Common in young adults and children

Aetiology

  • Exact cause unknown
  • Associated with retinoblastoma gene and p53 translocation

Location

  • Intramedullary meta-diaphyseal junction origin is classic
  • Most common around the knee
  • Less common in proximal humerus, proximal femur, and pelvis

Presentation

  • Short history of pain
  • Mass
  • Symptoms may appear after an acute injury
  • Pathologic fracture in 10% of cases
  • 20% of patients have lung metastases at presentation

Imaging

XR

  • Simultaneous bone formation and lysis
  • Codman’s triangle (elevated periosteum)
  • Sunray spicules (tumor invasion into bone remodeling)
  • Lesions may be sclerotic, lytic, or mixed
  • CXR: Evaluate for pulmonary metastases #### MRI
  • Neurovascular involvement, surgical planning, and skip lesion assessment #### Bone Scan
  • Screens for bony metastases and skip lesions #### CT
  • Used for staging the chest, abdomen, and pelvis

Histology

  • Intramedullary osteosarcoma is high grade
  • All osteosarcomas originate from spindle cells
  • Diagnosis requires the presence of malignant osteoid
  • Features include:
    • Pleomorphic cells (altered size and shape)
    • Dark-stained nuclei
    • Poorly differentiated nuclei
    • High mitotic activity
    • Invasion into surrounding tissues

Management

  • Neo-adjuvant chemotherapy: Administered for 6–12 weeks to induce tumor necrosis and stabilize the reactive zone
  • Re-staging of tumor
  • Surgical excision: Wide or radical excision based on stage and tumor necrosis
  • Adjuvant chemotherapy
  • Amputation: Only if the limb is unsalvageable
  • Limb salvage: Achievable in 90% of cases today
  • Lung metastases: Isolated cases are potentially resectable

Outcomes

Poor Prognostic Indicators

  1. High LDH levels
  2. High alkaline phosphatase levels
  3. No DNA alteration post-chemotherapy
  4. Vascular invasion
  5. Metastases at presentation (bone worse than lung)
  6. Local recurrence or incomplete margins
  7. Expression of P-glycoprotein
  8. Absence of anti-shock protein 90 antibodies post-chemotherapy
  9. Presentation with pathologic fractures (higher recurrence rates)
  10. Pelvic location

Good Prognostic Indicators

  1. No metastases and intracompartmental at presentation
  2. 90% tumor necrosis after neo-adjuvant chemotherapy

Outcome Statistics

  • Overall 5-year survival: 70%
  • Pelvic osteosarcoma 5-year survival: 25%
  • Metastatic presentation 5-year survival: 20%
  • Local recurrence and bone metastases indicate poor long-term survival

Intramedullary, Paraosteal, and Periosteal Osteosarcoma

Osteosarcoma Subtypes

Subtype Grade Location Notes
Paraosteal Low Distal femur (75%) Surface of bone, lobulated dense lesion like osteochondroma
95% survival with wide resection
Periosteal Intermediate Tibia or femur diaphysis Extensive sunray spiculing, chondroid-like appearance, produces cartilage and osteoid
Telangiectatic High Intramedullary Lytic lesion with blood-filled spaces, resembles aneurysmal bone cyst
Paget’s Osteosarcoma High Femur, pelvis, craniofacial Poor prognosis, often polyostotic, occurs in elderly patients
Post-Radiation OS High Prior radiotherapy site Mean delay of 17 years, very aggressive
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