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

Stage Grade (G) Anatomy (T) Mets (M) Classification
Ia Low (G1) IC (T0) M0 G1, T0, M0
Ib Low (G1) EC (T1) M0 G1, T1, M0
IIa High (G2) IC (T0) M0 G2, T0, M0
IIb High (G2) EC (T1) M0 G2, T1, M0
IIIa Any IC (T0) M1 G1/2, T0, M1
IIIb Any EC (T1) M1 G1/2, T1, M1
  • Stages I are all low grade
  • Stage II are all high grade
  • Stages III all have metastases

Enneking Classification of Benign Bone Tumours

Stage Activity Examples
1 Latent Osteoid Osteoma, Enchondroma, NOF
2 Active Chondroblastoma, UBC
3 Aggressive GCT, ABC

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

Level Description
Intralesional Through the tumour itself; 100% local recurrence; option for palliation of mass effect
Marginal Through the pseudo-capsule (reactive zone); 50% local recurrence rate
Wide (en bloc) Intracompartmental resection with a cuff of normal tissue attached; <10% local recurrence
Radical Extracompartmental resection; entire compartment and all tissues resected

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
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