Chondroblastic Osteosarcoma
Synonyms: Osteosarcoma, chondroblastic variant
Chondroblastic OS shows predominant presence of chondroid matrix
Quick Facts
Behaviour
Malignant
Category
Bone
Grade
High
Synonyms
- Osteosarcoma
- chondroblastic variant
Category
Bone
Behaviour
Malignant
Grade
High
Gender
Male (1.3:1)
Tissue of Origin
Bone
Epidemiology
- Second most common subtype of conventional osteosarcoma (25%)
- Peak incidence 2nd decade - most cases 10-14 years
- Male predominance
- Same demographics as conventional osteosarcoma
Clinical Features
- Pain and swelling at affected site
- Pathological fracture in 10%
- Decreased range of motion of adjacent joint
- Mass effect on surrounding structures
Location
- Metaphysis of long bones
- Distal femur most common
- Proximal tibia, proximal humerus
- Axial skeleton in older patients
Imaging
- Plain radiograph: Mixed lytic-sclerotic lesion with aggressive periosteal reaction
- Predominantly chondroid matrix (rings and arcs, popcorn mineralisation)
- Cortical destruction and soft tissue mass
- MRI: heterogeneous signal with cartilaginous lobules
Pathology
- High-grade sarcomatous stroma with abundant malignant cartilage
- Osteoid production by tumour cells (required for diagnosis)
- Nuclear pleomorphism and High mitotic activity
- Areas of necrosis common after chemotherapy
Genetics
- Complex karyotype
- TP53 mutations
- RB1 alterations
- CDK4 and MDM2 amplification in some cases
Treatment
- Neoadjuvant chemotherapy (MAP: methotrexate, doxorubicin, cisplatin)
- Wide surgical resection
- Adjuvant chemotherapy based on histological response
- Poor response to chemotherapy more common in chondroblastic variant
Prognosis
- 5-year survival 60-70% for localised disease
- Chondroblastic variant may have slightly worse chemotherapy response
- Pulmonary metastases in 30-40%
- Good histological response (>90% necrosis) associated with better outcome
Key Points
- Chondroblastic OS shows predominant presence of chondroid matrix
- May resemble chondrosarcoma - osteoid must be identified
- Often shows poorer chemotherapy response than other OS subtypes
- Distinguishing from dedifferentiated chondrosarcoma is critical (different treatment and prognosis)
- IDH1/2 mutation testing helps exclude chondrosarcoma
Workup - Blood Tests
- FBC, U&E, LFTs, Bone profile - baseline and pre-chemotherapy
- Alkaline phosphatase - tumour marker; elevated in 50%
- LDH - prognostic marker
- Coagulation screen - pre-operative
Workup - Local Imaging
- Plain radiograph
- MRI of whole bone with gadolinium
Workup - Biopsy
Core needle biopsy at sarcoma centre - planned to allow en bloc excision of tract
Workup - Staging
- CT chest
- PET-CT
Workup - Other
- Echocardiogram + audiometry baseline pre-chemotherapy
- MDT at Bone sarcoma specialist centre
- Fertility counselling pre-chemotherapy
Follow-up Summary
Histological response to MAP chemotherapy is reviewed at surgery - guides adjuvant strategy
Limb function assessed using MSTS/TESS scores at each visit
Medical disclaimer
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