Osteoblastic Osteosarcoma
Synonyms: Osteosarcoma, osteoblastic variant; sclerosing osteosarcoma
Most common conventional OS subtype - 'classic' osteosarcoma
Quick Facts
Behaviour
Malignant
Category
Bone
Grade
High
Synonyms
- Osteosarcoma
- osteoblastic variant; sclerosing osteosarcoma
Category
Bone
Behaviour
Malignant
Grade
High
Gender
Male (1.5:1)
Tissue of Origin
Bone
Epidemiology
- Most common subtype of conventional osteosarcoma (50%)
- Peak incidence in 2nd decade
- Bimodal age distribution: adolescents and elderly (secondary OS)
Clinical Features
- Pain and swelling at affected site
- Decreased range of motion of adjacent joint
- Pathological fracture in 10%
- Palpable firm mass
Location
- Metaphysis of long bones
- Distal femur (40%), proximal tibia (20%), proximal humerus (10%)
- Axial skeleton in older patients
- Jaws in secondary osteosarcoma
Imaging
- Dense sclerotic 'ivory' lesion with aggressive periosteal reaction
- Sunburst periosteal reaction and Codman triangle
- Cortical destruction and soft tissue mass
- MRI: heterogeneous with prominent Low-signal sclerotic areas
Pathology
- High-grade sarcomatous stroma producing abundant osteoid/Bone
- Densely mineralised tumour matrix
- High nuclear grade and mitotic activity
- Necrosis proportional to chemotherapy response
Genetics
- Complex karyotype
- TP53, RB1 alterations common
- MDM2/CDK4 amplification in secondary osteosarcoma
- ATRX mutations
Treatment
- Neoadjuvant MAP chemotherapy (methotrexate, doxorubicin, cisplatin)
- Wide surgical resection - limb salvage in 85%
- Adjuvant chemotherapy based on histological response (>90% necrosis = good response)
- Amputation for unresectable or neuroVascular involvement
Prognosis
- 5-year survival 60–70% for localised disease
- Good histological response (>90% necrosis) is the most important prognostic factor
- Pulmonary metastases in 30–40%
- Paget-related OS: very poor prognosis (10% 5-year survival)
Key Points
- Most common conventional OS subtype - 'classic' osteosarcoma
- Dense ivory sclerosis on X-ray is Highly characteristic
- Histological response to neoadjuvant chemotherapy is the single most important prognostic factor
- High-dose methotrexate is uniquely active in OS - not used in other sarcomas
Workup - Blood Tests
- FBC, U&E, LFTs, Bone profile - baseline and pre-chemotherapy
- Alkaline phosphatase - elevated; tumour marker
- LDH - prognostic marker
- Coagulation screen
Workup - Local Imaging
- Plain radiograph
- MRI with gadolinium of whole bone
Workup - Biopsy
- Core needle biopsy at sarcoma centre
- Histology: High-grade osteosarcoma with abundant mineralised osteoid
- MDM2/CDK4 FISH - negative (excludes secondary OS associated with amplification)
- IHC: TP53, MDM2, H3K27me3 panel
Workup - Staging
- CT chest - pulmonary metastases
- Wole-body MRI - skip lesions and bone metastases
- PET-CT
Workup - Other
- Echocardiogram and audiometry pre-chemotherapy
- Fertility counselling - pre-treatment
- MDT at Bone sarcoma specialist centre (NICE IOG) mandatory
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
Medical disclaimer
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