Synonyms

• Sarcoma complicating Paget disease
• Pagetic osteosarcoma

Category

Bone

Behaviour

Malignant

Grade

High

Gender

Male

Tissue of Origin

Bone

Epidemiology

• Rare but important complication of Paget disease of Bone
• Occurs in 1% of patients with Paget disease
• Peak incidence in 7th–8th decades
• Male predominance (reflecting Paget disease demographics)

Clinical Features

• New or worsening pain in patient with known Paget disease
• Rapidly enlarging mass within pagetic Bone
• Pathological fracture
• May be multifocal (due to widespread Paget disease)

Location

• Pelvis most common (40%)
• Femur (25%)
• Humerus
• Skull (less common)

Imaging

• Aggressive lytic destruction within background of pagetic Bone (expanded, coarse trabeculation)
• Cortical breakthrough and soft tissue mass
• MRI: heterogeneous mass within abnormal pagetic Bone
• Bone scan: markedly hot - change from baseline pagetic uptake

Pathology

• High-grade osteosarcoma (osteoblastic, fibroblastic, or MFH-like) on background of pagetic Bone
• Background Bone shows characteristic pagetic mosaic cement lines
• TP53 mutation common
• MDM2 amplification

Genetics

• TP53 mutations in majority
• MDM2 amplification (different mechanism from Paget disease itself)
• Complex karyotype
• Paget disease driven by SQSTM1 (p62) mutations and RANKL pathway

Treatment

• Wide surgical resection - technically challenging due to abnormal pagetic Vascularity
• Chemotherapy (doxorubicin/ifosfamide): poor response
• Radiotherapy: poor local control
• Palliative intent in many patients due to age and comorbidities

Prognosis

• Very poor: median survival 12 months
• 5-year survival <10%
• Much worse prognosis than conventional osteosarcoma
• Poor response to chemotherapy

Key Points

• New pain in Paget disease should prompt urgent imaging to exclude sarcomatous transformation
• 5-year survival <10% - much worse than conventional osteosarcoma
• Bisphosphonate treatment of Paget disease may reduce (but not eliminate) risk of transformation
• Multidisciplinary planning essential - surgery most important modality

Workup - Blood Tests

• FBC, U&E, LFTs, Bone profile - baseline and pre-operative
• Alkaline phosphatase - elevated (from underlying Paget disease)
• LDH - prognostic marker

Workup - Local Imaging

• Plain radiograph - aggressive lytic destruction within background pagetic Bone (expanded with coarse trabeculation)
• MRI primary site with gadolinium - local staging; heterogeneous mass within abnormal pagetic Bone
• CT chest/abdomen/pelvis - metastatic staging
• Bone scan - shows marked increase in uptake from baseline Paget disease

Workup - Biopsy

• Core needle biopsy - confirm sarcomatous transformation (High-grade osteosarcoma-like lesion)
• IHC: TP53 mutations common; MDM2 amplification
• Histology: High-grade sarcoma on background of characteristic pagetic Bone (mosaic cement lines)

Workup - Staging

• CT chest/abdomen/pelvis - metastatic disease
• PET-CT - systemic staging

Follow-up Summary

• Years 1–2: 3–4 monthly clinical review + CXR; xray of primary site
• Years 3–5: 6-monthly clinical review + CXR
• Years 6–10: Annual clinical review + CXR
• Discharge at 10 years with documented self-monitoring advice