Principles of Musculoskeletal Oncology

Principles: Tumor Basics - Spotting the Suspects

• Tumor Types:
  • Primary: Arise from MSK tissues (bone, cartilage, soft tissue).
    • Benign: Well-defined, slow-growing, e.g., Osteochondroma.
    • Malignant (Sarcomas): Invasive, potential to metastasize, e.g., Osteosarcoma, Ewing's sarcoma.
  • Secondary: Metastases from other cancers (e.g., breast, lung, prostate). Most common bone tumors in adults.
• Clinical Clues - Red Flags ⚠️:
  • Pain: Persistent, night pain, rest pain, unrelated to activity, progressive.
  • Swelling/Mass:
    • Rapidly enlarging.
    • Size >5 cm.
    • Deep to fascia, fixed.
    • Warmth, tenderness.
  • Pathological fracture (fracture with minimal/no trauma).
  • Unexplained weight loss, fever (especially with Ewing's, Lymphoma).
  • History of prior malignancy.

⭐ Most common overall bone tumor in adults is metastasis. Most common primary malignant bone tumor is Osteosarcoma.

Principles: Diagnostics - The Inside Scoop

• Imaging Modalities:

  • X-ray: Initial. Defines lesion (lytic/sclerotic), margins, periosteal reactions (Codman's, sunburst).
  • MRI: Local staging: soft tissue/marrow extent, skip lesions, neurovascular (NV) proximity. T1 (anatomy), T2/STIR (tumor/edema).
  • CT Scan: Best for cortical bone detail, matrix mineralization. Chest CT for lung metastases.
  • Bone Scan ($^{99m}Tc-MDP$): Polyostotic disease. PET-CT ($^{18}F-FDG$): Staging, response, recurrence.

• Biopsy: Tissue is the Issue

  • ⭐ Improper biopsy of suspected sarcoma compromises limb salvage; perform at definitive treatment center by operating surgeon.

  • Key Principles:

-   Types: Core needle (image-guided, standard), Incisional (open). FNA (limited). Excisional (rarely, small benign).

Principles: Staging - Sizing Up the Foe

• Purpose: Guides prognosis & treatment strategy.
• Enneking System (Surgical Staging System - SSS): Widely used for musculoskeletal tumors.
  • Benign (Arabic numerals: 1, 2, 3):
    • 1 (Latent): Asymptomatic, often incidental (e.g., Non-ossifying fibroma).
    • 2 (Active): Symptomatic, growing, contained within bone (e.g., Aneurysmal Bone Cyst).
    • 3 (Aggressive): Locally destructive, may breach cortex (e.g., Giant Cell Tumor).
  • Malignant (Roman numerals: I, II, III): Based on Grade (G), Site (T), Metastasis (M).
    • G: G1 (Low grade), G2 (High grade)
    • T: T1 (Intracompartmental), T2 (Extracompartmental)
    • M: M0 (No metastasis), M1 (Metastasis)
    • Stage IA: G1 T1 M0
    • Stage IB: G1 T2 M0
    • Stage IIA: G2 T1 M0
    • Stage IIB: G2 T2 M0
    • Stage III: Any G, Any T, M1 (Presence of regional or distant metastasis)

⭐ Enneking Stage III (M1) signifies metastasis, which is the most critical factor, overriding grade (G) and local tumor extent (T) for this stage.

Principles: Treatment - Battle Plan

• Core Strategy: Multidisciplinary Team (MDT) (Ortho Onco, Med Onco, Rad Onco, Pathologist, Radiologist) is paramount.
• Goal: Cure, preserve limb function, maintain Quality of Life (QoL).

• Surgical Principles:
  • Margins: Key to local control. Types: Intralesional, Marginal, Wide, Radical.
    • Wide Excision: Tumor + cuff of normal tissue (standard for most sarcomas).
    • Radical Resection: Entire compartment removed.
  • Limb Salvage Surgery (LSS): Preferred if oncologically safe & functional outcome achievable.
    • Reconstruction options: Endoprosthesis, allografts, arthroplasty, arthrodesis.
• Chemotherapy:
  • Neoadjuvant: Osteosarcoma, Ewing's Sarcoma (↓tumor size, assess response, treat micromets).
  • Adjuvant: Eradicate residual micrometastases.
• Radiotherapy (RT):
  • Definitive or adjuvant for radiosensitive tumors (e.g., Ewing's Sarcoma, Lymphoma).
  • Pre-operative or Post-operative for soft tissue sarcomas to improve local control.
  • Palliative for bone pain, spinal cord compression.

⭐ >90% tumor necrosis (e.g., Huvos Grade IV) after neoadjuvant chemotherapy in osteosarcoma indicates a good prognosis.

High‑Yield Points - ⚡ Biggest Takeaways

• Metastasis is the most common bone malignancy; primaries: Prostate, Breast, Kidney, Thyroid, Lung (PBKTL).
• Osteosarcoma: most common primary malignant bone tumor, then Chondrosarcoma, Ewing sarcoma.
• Osteochondroma: most common benign bone tumor. Benign tumors are more frequent than primary malignant.
• Red flags: night pain, palpable mass, pathological fracture.
• Crucial biopsy: needle preferred, tract resectable with definitive surgery.
• Treatment: Wide surgical excision for sarcomas; often multimodal (chemo, radio).