Principles of Bone Oncology

Enneking System – Staging System

• Benign or malignant
• Enneking system is a post-resection staging system, but:
  • Good approximation possible with a reliable biopsy and imaging
• For malignant tumours, components are:
  • Grade: High or low
  • Anatomic Features: Intra or extra-compartmental
  • Metastases: Present or not

Grade (G1, G2 – low or high grade)

• Grade determined by:
  • Degree of normal cell differentiation
  • Mitotic figures
  • Pleomorphism (variation in cell size and shape)

Features of High-Grade Tumours:

• High mitotic rate
• Poorly differentiated (correlates with metastases)
• Pleomorphism
• Necrotic dark nuclei
• High cell-matrix ratio
• High risk of metastasis

Anatomic Features – Intra or Extra-compartmental

• Intra-compartmental: Within the bone or fascial compartment
• Extra-compartmental: Breached the bone or fascial compartment
• T1 MRI is best for detecting intramedullary extent and skip lesions

Metastases

• Presence or absence
• Metastases automatically classify the tumour as Grade 3

Staging Table

• Stages I are all low grade
• Stage II are all high grade
• Stages III all have metastases

Enneking Classification of Benign Bone Tumours

Principles of Tumour Biopsy

Biopsy Types

• Incisional Biopsy
  • Open incision and removal of tissue samples
• Excisional Biopsy
  • Only for lesions where diagnosis is almost certain and with low chance of recurrence (e.g., lipoma)
  • Danger of recurrence with incomplete margins
• Percutaneous Biopsy
  • Fine needle aspiration for cytology (not as frequent in the UK as True Cut)
  • True Cut biopsy for core specimen:
    • More effective under CT or US guidance
    • Yields 97% accuracy with expert technique
    • Less detail about mitotic figures than incisional biopsy
    • Does not usually affect management

Principles of Performing an Incisional Biopsy

Planning

• Performed by or in accordance with the surgeon doing the definitive procedure
• Pathologist:
  • Should be consulted regarding the ideal biopsy location
  • Should be aware and ready to receive the biopsy
  • Should be skilled to perform all tests on the specimen

Surgical Technique

• Leave an excisable scar and biopsy tract (avoid transverse incisions)
• Approach should not violate further muscle compartments
• Meticulous haemostasis:
  • Use a tourniquet and release before closure
  • Drain out through the wound
• Approach through muscle preferred for tight closure

Sampling Specimen

• Take from soft rather than bony part
• Prefer peripheral over necrotic centre (plan this beforehand)
• Use frozen section to ensure sample is representative
• Send for MC&S and histology

Principles of Work-Up

History

• Atypical pain; night pain; pain not relieved by analgesia
• Neurological or vascular symptoms distally

Examination

• Examine NV structures
• Conduct normal examination of the mass
• Look for lymph nodes proximally
• Examine breasts, thyroid, chest, prostate, and kidneys if metastases are suspected

Laboratory Tests

• Depends on the differential diagnosis:
  • FBC, U&E, LFT, Clotting, CRP (mandatory)
  • LDH & Alk Phos (prognostic criteria in Osteosarcoma)
  • Myeloma screen in older patients; peripheral blood smear in younger patients
  • Urine analysis

Imaging

• X-ray (bone and chest)
• Skeletal survey for myeloma (often negative on bone scans)
• Bone scan
• MRI
• Staging CT (chest, abdomen, pelvis)

Important Descriptors of a Lesion

• Patient age
• Location in bone
• Monostotic or polyostotic
• Matrix:
  • Permeative
  • Sclerotic
  • Ground-glass
• Zone of transition:
  • Narrow (geographic)
  • Wide (indistinct)
• Periosteal reaction
• Soft tissue extent
• Effect on bone and bone's effect on the lesion:
  • Scalloped
  • Walled off
  • Expanded

Principles of Management

• All management should be coordinated by a bone tumour unit

Limb Salvage Versus Amputation

• Most limbs are salvageable with modern techniques and adjuvant therapy
• Do not compromise limb function or tumour eradication to salvage a limb
• Indications for amputation:
  • Neurovascular infiltration rendering tumour irresectable without significant limb damage
  • Extensive muscle invasion where resection compromises function
  • Pathologic fracture with wide dissemination of tumour

Levels of Resection

Adjuvant & Neo-Adjuvant Therapy

Chemotherapy

• Causes programmed cell death (apoptosis):
  • Direct DNA damage (e.g., alkylating agents)
  • Deplete cellular building blocks (e.g., 5-fluoropyrimidines)
  • Interfere with microtubule function (e.g., vinca alkaloids)
• Cochrane Review 2000:
  • Good for bony malignancy (e.g., Osteosarcoma, Ewing’s)
  • Minimal benefit for soft tissue malignancy unless highly chemosensitive (e.g., Rhabdomyosarcoma)
• Usual treatment protocol:
  • Neo-adjuvant therapy pre-operatively
  • Tumour re-staged, and surgery planned
  • Adjuvant chemotherapy post-operatively

Radiotherapy

• Direct DNA damage by free radicals
• Indications:
  • Radiosensitive tumours (e.g., Ewing’s, lymphoma, breast cancer)
  • Incomplete margins in difficult locations (e.g., spine, pelvis)
  • Metastatic pain
• Complications:
  • Post-irradiation sarcoma
  • Stress fracture
  • Wound problems
  • Fibrosis
  • Lymphedema

Reconstructive Options

Endoprosthesis

• Mainstay treatment; usually includes a joint
• Growing prostheses in children (magnet-based)
• Complications:
  • Extensive surgery
  • Loosening and wear
• Survival:
  • 70% at 5 years
  • With revision, up to 90% at 10 years

Autograft

• Most commonly fibula; can hypertrophy with weight-bearing
• Common in distal radius
• Used as a strut graft to augment other reconstruction methods

Allograft

• Massive allografts used but are dead bone
• Slow or no incorporation
• Infection risk and limited availability