MalignantBone
Dedifferentiated Chondrosarcoma
Synonyms: Dediff CS
High-grade, agressive chondrosarcoma associated with early metastatic spread
Quick Facts
Behaviour
Malignant
Category
Bone
Grade
High
Synonyms
Dediff CS
Category
Bone
Behaviour
Malignant
Grade
High
Gender
M = F
Tissue of Origin
Cartilage
Epidemiology
- 10% of chondrosarcomas
- Peak incidence in 6th-8th decades
- Older patients than conventional chondrosarcoma
Clinical Features
- Rapid onset of pain or swelling, may have a known chondroid lesion
- Pathological fracture common (25%)
- Often large tumour at presentation
- Rapid clinical deterioration
Location
- Pelvis and proximal femur most common
- Proximal humerus
- Distal femur
Imaging
- Plain radiograph: Bimorphic lesion: with cartilaginous component (rings/arcs calcification) and aggressive lytic component
- CT: calcified chondroid lobules + permeative lytic area
- MRI: High T2 chondroid component + aggressive sarcomatous component
Pathology
- Bimorphic histology: Low-grade chondrosarcoma juxtaposed with high-grade non-chondrosarcomatous sarcoma
- Abrupt transition (no gradual dedifferentiation)
- High-grade component: MFH-like, osteosarcoma-like, or fibrosarcoma-like
- IDH1/2 mutation in Low-grade component
Genetics
- IDH1 (R132) or IDH2 (R172) mutation in chondroid component
- Complex genomic alterations in dedifferentiated component
- CDKN2A loss, TP53 mutation in high-grade component
Treatment
- Wide surgical resection - primary treatment
- Adjuvant chemotherapy (doxorubicin/ifosfamide) for high-grade dedifferentiated component
- Chemotherapy response is limited
- Radiotherapy for unresectable disease
Prognosis
- Very poor: 5-year survival 10-25%
- Most patients die within 2 years of diagnosis
- Haematogenous metastasis to lungs in >80%
- Worst prognosis of all chondrosarcoma subtypes
Key Points
- High-grade, agressive chondrosarcoma associated with early metastatic spread
- Abrupt bimorphic histology is characteristic - unlike secondary high-grade sarcoma
- Very limited response to systemic therapy
- Prognosis dramatically worse than conventional chondrosarcoma
Workup - Blood Tests
- FBC, U&E, LFTs, Bone profile - pre-operative baseline
- Alkaline phosphatase
- LDH
Workup - Local Imaging
- Plain radiograph
- MRI with contrast of whole bone
- CT to assess bony detail
Workup - Biopsy
Core needle biopsy - must sample both components (chondroid and high-grade)
Workup - Staging
- CT chest - metastases present in 10-15% at diagnosis
- Whole-body MRI or PET-CT
Workup - Other
MDM discussion at a sarcoma centre
Follow-up Summary
Medical disclaimer
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