Giant Cell Tumor of Bone (GCTB)

Epidemiology

• Peak incidence: 20-40 years of age (skeletally mature adults)
• Slight female predominance
• Rare in skeletally immature patients
• Typically solitary; 1-2% of cases present with multicentric (synchronous or metachronous) lesions
• Campbell's Operative Orthopaedics 15th Ed 2026

Pathogenesis / Molecular Basis

1. Neoplastic stromal cells overexpress RANKL (Receptor Activator of Nuclear Factor kB Ligand)
2. RANKL drives proliferation and differentiation of osteoclast precursors into mature, functioning osteoclasts
3. The abundant osteoclasts - not the neoplastic cells themselves - destroy bone through local resorption
4. Normal osteoblast-osteoclast feedback is lost, resulting in progressive, destructive bone resorption
5. The neoplastic stromal cells harbor mutations in H3-3A (the gene encoding histone 3.3, a chromatin packaging protein) - the mechanism by which this drives tumorigenesis remains unclear

• Robbins, Cotran & Kumar Pathologic Basis of Disease; Robbins & Kumar Basic Pathology

Location

• Epiphyses of long bones - this is the hallmark location, distinguishing GCTB from most other bone tumors
• Most common sites (in order):
  1. Distal femur
  2. Proximal tibia (these two together constitute the majority - "around the knee")
  3. Distal radius (tends to be more aggressive)
  4. Sacrum (for axial involvement)
  5. Spinal involvement otherwise uncommon
• Lesion abuts the subchondral bone and may extend into the metaphysis
• In skeletally immature patients (rare), arises in the metaphysis and likely extends into the epiphysis after physeal closure

Clinical Features

• Pain - the most common symptom; initially activity-related, later at rest
• Pathologic fracture - present in 10-30% of patients at initial diagnosis
• Arthritis-like symptoms due to proximity to the joint
• Swelling over the affected area
• Rarely: intraarticular extension (subchondral bone usually remains intact)

Imaging

Plain Radiograph

• Purely lytic (radiolucent), no matrix calcification
• Eccentric epiphyseal location, extending to or abutting subchondral bone
• Zone of transition may be poorly defined (aggressive lesions) or show a partial rim of reactive bone (less aggressive)
• Cortical expansion or breakthrough common
• Soft-tissue extension visible in aggressive cases

FIG. 19.24 - Giant cell tumor: purely lytic, expansile lesion with cortical destruction and pathologic fracture (Robbins & Kumar Basic Pathology)

MRI

• T1: dark (low signal)
• T2: bright (high signal)
• Fluid-fluid levels visible in ~20% of cases - indicates secondary aneurysmal bone cyst (ABC) component
• Best modality to determine intra-osseous and soft-tissue extent
• Campbell's Operative Orthopaedics 15th Ed 2026

Pathology / Histology

Gross

• Large, red-brown mass (due to hemosiderin and vascular stroma)
• Frequently undergoes cystic degeneration
• Destroys overlying cortex, creating a bulging soft-tissue mass bounded by a thin shell of reactive bone

Microscopy

• Osteoclast-type giant cells with 40-100+ nuclei per cell - distributed uniformly throughout the lesion
• Key diagnostic feature: the nuclei of the mononuclear stromal cells are identical to the nuclei within the giant cells - this helps distinguish GCTB from other giant-cell-containing lesions
• Background: uniform oval mononuclear stromal cells (the true neoplastic component)
• May show: storiform spindle cell areas, reactive bone formation, foamy macrophages, secondary ABC changes
• Necrosis and mitotic activity may be prominent
• Histologic grading has no prognostic significance - no grading system has been validated

FIG. 19.25 - Giant cell tumor: abundant multinucleate giant cells admixed with mononuclear stromal cells (Robbins & Kumar Basic Pathology)

Staging (Enneking / Campanacci)

• Stage 1 (Latent/Inactive): well-defined margin with reactive bone rim; intracortical
• Stage 2 (Active): expanded cortex, well-marginated; most common at presentation
• Stage 3 (Aggressive): cortical destruction, soft-tissue extension; poorly marginated

Malignant Giant Cell Tumor of Bone (MGCTB)

• Primary MGCTB: sarcomatous cells identified alongside conventional GCTB at initial biopsy
• Secondary MGCTB: sarcomatous transformation in a previously treated GCTB, often years later; strongly associated with prior radiotherapy
• Most common sarcoma subtype: osteosarcoma
• Radiographic and clinical features indistinguishable from aggressive conventional GCTB
• Definitive diagnosis requires biopsy

Treatment

Intralesional Curettage (Standard)

• Extended/aggressive curettage with power burr (enlarging cavity 1-2 cm in all directions) is the standard surgical approach
• Cortical window must be at least as large as the lesion to prevent "leaving tumor around the corner"
• Recurrence rates historically >50% with simple curettage; with modern technique (MRI-guided extent, extended curettage + adjuvants): 5-15%

Adjuvants

• Argon beam coagulator (preferred at many centers - effective, easy, low complication rate)
• Phenol or liquid nitrogen - historically used but associated with pathologic fracture, wound healing problems, and nerve injury
• Bisphosphonates (local or systemic) - preliminary evidence suggests may reduce recurrence

Cavity Filling

• Methyl methacrylate bone cement (preferred): provides immediate stability, allows detection of recurrence (appears as expanding radiolucency adjacent to cement), may kill residual cells via polymerization heat
• Autograft / allograft bone / artificial substitutes: restore bone stock but require prolonged joint protection and make recurrence detection harder
• Cement can be reinforced with crossed or divergent screws, or a periarticular plate

Wide Resection

• Stage 3 tumors unresponsive to curettage
• Recurrent lesions
• Tumors where curettage would be inadequate (e.g., distal radius - primary resection with proximal fibular autograft reconstruction)
• Reconstructive options: hemicondylar osteoarticular allograft, rotating hinge endoprosthesis

Denosumab (RANKL Inhibitor)

• Highly effective medical treatment by blocking RANKL - removes the osteoclast-stimulating signal
• Induces tumor reduction and bone formation
• Indications: unresectable tumors, resection would cause significant functional morbidity or deformity, recurrent disease
• Does not eliminate the neoplastic stromal cells; disease can recur after cessation
• Standard of care for surgically challenging GCTB
• Campbell's Operative Orthopaedics 15th Ed 2026; Robbins & Kumar Basic Pathology

Prognosis and Metastasis

• Pulmonary metastases ("benign metastasizing GCT") retain benign histology; some spontaneously regress, others remain asymptomatic; most can be cured by surgical excision of metastases
• Risk factors for pulmonary metastasis: stage 3 disease, recurrent tumors, aggressive radiographic features

Differential Diagnosis (Other Giant-Cell-Containing Lesions)

Recent Evidence

• A 2024 meta-analysis (PMID 39236154) of 1,454 patients found bone cement associated with lower recurrence compared to bone graft after intralesional curettage
• A 2024 systematic review (PMID 38711180) on surgical adjuvants confirms extended curettage + adjuvant significantly reduces local recurrence over simple curettage
• Heat treatment (radiofrequency ablation, cryotherapy) is being studied as an adjuvant; a 2023 systematic review (PMID 37726111) found promising results but noted heterogeneity in available data