Fibroblastic Osteosarcoma
Synonyms: Osteosarcoma, fibroblastic variant
Predominantly lytic lesion - may be confused with fibrosarcoma of Bone or MFH
Quick Facts
Behaviour
Malignant
Category
Bone
Grade
High
Synonyms
- Osteosarcoma
- fibroblastic variant
Category
Bone
Behaviour
Malignant
Grade
High
Gender
Male
Tissue of Origin
Bone
Epidemiology
- Accounts for 25% of conventional osteosarcoma
- Peak incidence in 2nd decade
- Same demographics as conventional osteosarcoma
Clinical Features
- Pain and swelling at affected site
- Pathological fracture in 10%
- May grow faster than chondroblastic variant
- Decreased range of motion of adjacent joint
Location
- Metaphysis of long bones
- Distal femur most common
- Proximal tibia, proximal humerus
- Axial skeleton in older patients
Imaging
- Predominantly lytic with minimal matrix mineralisation
- Aggressive periosteal reaction (Codman triangle, sunburst)
- Cortical destruction and soft tissue mass
- MRI: large heterogeneous mass with extensive soft tissue involvement
Pathology
- High-grade spindle cell sarcoma with herringBone/fascicular pattern
- Osteoid production by tumour cells (essential for diagnosis)
- Minimal chondroid matrix
- High nuclear grade and mitotic activity
Genetics
- Complex karyotype
- TP53 and RB1 alterations common
- MDM2/CDK4 amplification in some cases
- ATRX mutations
Treatment
- Neoadjuvant MAP chemotherapy (methotrexate, doxorubicin, cisplatin)
- Wide surgical resection - limb salvage when feasible
- Adjuvant chemotherapy based on histological response
- Good response to chemotherapy - generally better than chondroblastic variant
Prognosis
- 5-year survival 60–70% for localised disease
- Generally better chemotherapy response than chondroblastic variant
- Pulmonary metastases in 30–40%
- Good histological response (>90% necrosis) is the most important prognostic factor
Key Points
- Predominantly lytic lesion - may be confused with fibrosarcoma of Bone or MFH
- Identification of osteoid (even focal) is required for OS diagnosis
- Generally more chemosensitive than chondroblastic OS
- Must be distinguished from High-grade surface osteosarcoma
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
Workup - Local Imaging
- Plain radiograph
- MRI whole bone with gadolinium - local staging, medullary and soft tissue extent
Workup - Biopsy
- Core needle biopsy at sarcoma centre - en bloc excision of tract required
- Histology: High-grade spindle cell sarcoma with osteoid production
- MDM2/CDK4 FISH - negative (excludes parosteal OS)
- IHC panel: TP53, MDM2, H3K27me3
Workup - Staging
- CT chest - pulmonary metastases
- PET-CT - skeletal staging
Workup - Other
- Echocardiogram and audiometry baseline pre-chemotherapy
- MDT at Bone sarcoma specialist centre (NICE IOG)
Follow-up Summary
- 1
Year 1
Post-operative visit within first 6 weeks (if primary surgery); 2-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry (U&E, LFT, Ca, PO4, Mg, HCO3); end of Year 1 - gonadal function (males: testosterone, LH, FSH; females: oestradiol, LH, FSH)
- 2
Years 2–3
3-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 2 - MUGA or ECHO
- 3
Year 4
6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 4 - MUGA or ECHO
- 4
Year 5
6-monthly clinical examination, CXR, plain films of primary site; annual blood biochemistry
- 5
Years 6–10
Annual clinical examination, CXR, plain films of primary site; annual blood biochemistry; end of Year 6 - MUGA or ECHO
- 6
Discharge at 10 years after surgery
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