Osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor, characterized by direct formation of osteoid or immature bone by malignant mesenchymal cells.

Epidemiology

Bimodal Age Distribution

Anatomic Considerations for Tumor Location

Metaphyseal Predilection:

• Osteosarcoma arises from primitive mesenchymal bone-forming cells
• Metaphyses have highest osteoblastic activity during growth
• Rich blood supply to metaphyses facilitates tumor growth
• Growth plate initially acts as barrier to epiphyseal extension

Compartmental Anatomy

Tumor Extension Patterns:

Neurovascular Relationships

History

Physical Examination

Systematic Assessment:

1. Inspection:

   • Swelling/mass location
   • Skin changes (rare, late)
   • Muscle wasting (adjacent)
   • Limb length (if growth plate involved)

2. Palpation:

   • Mass characteristics: Firm, fixed to bone, tender
   • Warmth (increased vascularity)
   • Range of motion (reduced if near joint)
   • Lymph nodes (rarely involved - under 3%)

3. Neurovascular:

   • Pulses (rarely compromised)
   • Sensation (late involvement)
   • Motor function
   • Compartment tension

Differential Diagnosis

Imaging Protocol

Plain RadiographsMRIStaging Studies

First-Line Investigation - Essential Characteristics:

1. Location:

   • Metaphyseal (most common)
   • Eccentric or central

2. Matrix:

   • Osteoid production (cloud-like density)
   • "Cumulus cloud" appearance
   • Dense sclerotic areas

3. Periosteal Reaction:

   • Sunburst/Spiculated: Pathognomonic
   • Codman Triangle: Elevated periosteum at margins
   • Indicates aggressive behavior

4. Margins:

   • Permeative/moth-eaten (aggressive)
   • Wide zone of transition
   • Cortical destruction

5. Soft Tissue:

   • Extraosseous mass
   • May show calcification

These findings together create the classic "aggressive bone lesion" appearance.

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Essential for Surgical Planning

• T1-weighted: Tumor extent, marrow replacement (low signal)
• T2/STIR: Edema, soft tissue extent (high signal)
• Gadolinium: Enhancement patterns, viable tumor

Critical Information

1. Intramedullary extent - Proximal resection level
2. Skip lesions - Must image ENTIRE bone
3. Neurovascular involvement
4. Joint involvement
5. Soft tissue extent

Skip Lesions

Skip lesions occur in 1-5% of osteosarcomas. Always request MRI of ENTIRE bone. Missing a skip lesion leads to inadequate resection and recurrence.

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Systemic Staging Protocol

1. CT Chest:

   • Pulmonary metastases (most common site - 80% of mets)
   • Thin-cut (1-2mm) essential
   • Present at diagnosis in 15-20%

2. Bone Scan:

   • Detects bone metastases
   • Polyostotic disease
   • Hot uptake in primary tumor

3. PET-CT:

   • Increasingly used
   • Combines metabolic and anatomic data
   • Useful for response assessment

Laboratory Studies

• Alkaline phosphatase (elevated in 50%, prognostic)
• LDH (elevated indicates poor prognosis)
• Full blood count, renal/liver function (pre-chemo baseline)

Complete staging is essential before initiating treatment.

Biopsy Principles

Biopsy Technique:

Biopsy Rules:

1. Longitudinal incision along planned resection
2. Avoid contaminating neurovascular structures
3. Through muscle (not between compartments)
4. Meticulous hemostasis
5. Mark biopsy site for excision

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Chemotherapy Protocol

Chemotherapy Toxicities

Indications for Chemotherapy

Surgical Principles

Margin Requirements:

• Wide Margin: Minimum 1-2cm of bone beyond tumor
• Cuff of Normal Tissue: Must include reactive zone
• Biopsy Tract: Excise with specimen
• Skip Lesions: Must be included in resection

Limb Salvage Options

Amputation Considerations

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Chemotherapy Complications

Surgical Complications

Local Recurrence

Immediate Postoperative Period

Rehabilitation Protocol

Follow-up Surveillance

Survival Rates

Prognostic Factors

Functional Outcomes

The risk-factors card lists Li-Fraumeni, hereditary retinoblastoma and Rothmund-Thomson and notes a 2-5% secondary-malignancy rate, but the topic never develops the genetics - yet the germline predisposition syndromes are high-yield and change how you counsel a young patient and their family. (Paget-associated secondary osteosarcoma is developed in the paget-sarcoma topic; this is the inherited/germline dimension.)

• Li-Fraumeni syndrome (germline TP53). A loss-of-function germline mutation in the TP53 tumour-suppressor gives a very high lifetime cancer risk, with osteosarcoma one of the classic component tumours (alongside soft-tissue sarcoma, breast cancer, brain tumours, adrenocortical carcinoma and leukaemia). An osteosarcoma in a very young child, multifocal disease, or a strong family cancer history should prompt consideration of Li-Fraumeni, referral for genetic counselling and germline testing, and awareness of the lifelong multi-cancer surveillance these families need.
• Hereditary retinoblastoma (germline RB1). Survivors of bilateral (germline) retinoblastoma carry a markedly increased risk of second cancers, and osteosarcoma is the single most common second malignancy - both spontaneously and, importantly, within a prior radiotherapy field because the retinoblastoma-treatment RB1-deficient tissue is radiosensitive. A history of childhood retinoblastoma in an osteosarcoma patient is a major red flag.
• RecQ-helicase (DNA-repair) syndromes. Rothmund-Thomson syndrome (RECQL4), and to a lesser extent Bloom and Werner syndromes, are autosomal-recessive DNA-repair disorders with an increased osteosarcoma risk - typically presenting younger and sometimes multifocally.
• Why it matters clinically. Recognising a predisposition syndrome triggers germline testing and genetic counselling, changes surveillance (the patient and relatives are at risk of further cancers), and informs treatment caution - particularly minimising radiotherapy exposure in RB1 and DNA-repair-defective patients, who are prone to radiation-induced second tumours.

The topic lists prior radiation therapy as a risk factor and a 2-5% secondary-malignancy rate, and notes a secondary peak in older adults, but never develops radiation-induced sarcoma - a discrete, examinable entity with its own diagnostic criteria.

• What it is. A secondary sarcoma arising in a previously irradiated field, usually years to decades after radiotherapy for a different (often childhood) cancer. Osteosarcoma is the most common radiation-induced bone sarcoma, and the risk is dose-dependent and higher in genetically susceptible patients (notably germline RB1 retinoblastoma survivors and DNA-repair syndromes).
• The Cahan criteria (how it is defined). A post-radiation sarcoma is classically diagnosed when: (1) the tumour arises within the prior radiation field; (2) there is a latency period (typically several years - often five or more); (3) the sarcoma is histologically proven and distinct from the original irradiated lesion; and (4) the irradiated tissue was normal, or a different tumour type, before radiotherapy.
• Why it matters. Radiation-induced osteosarcoma tends to occur at older ages and in axial or previously-irradiated sites, is often higher-stage at presentation, and carries a worse prognosis than conventional extremity osteosarcoma. The surgical principles are unchanged (wide resection, chemotherapy for high-grade disease), but re-irradiated, scarred, hypovascular tissue makes resection and reconstruction harder - and it reinforces the case for minimising and carefully planning radiotherapy in children, especially those with a genetic predisposition.

Global Epidemiology

• Incidence approximately 3-4 per million per year worldwide, the most common primary bone sarcoma of childhood and adolescence
• Bimodal distribution: a dominant adolescent peak (skeletal growth spurt) and a smaller secondary peak over 60 (often Paget-associated or radiation-induced), the latter carrying a markedly worse prognosis
• Outcomes plateaued internationally since the 1980s: 60-70% 5-year survival for localised disease, 20-30% for metastatic disease at presentation, with no major survival gain from chemotherapy intensification (EURAMOS-1)

Major Guidelines Side by Side

Registry and Network Evidence

• Cooperative groups (COSS, COG, EOI, SSG) feeding the EURAMOS collaboration provide the strongest randomised evidence base
• Bone-tumour endoprosthesis outcome data are pooled through specialist-centre series (eg Birmingham/Royal Orthopaedic Hospital) rather than national joint registries, which exclude tumour implants
• International tumour banking and biobanking underpin ongoing molecular and trial work

High- vs Limited-Resource Practice Variation

• High-resource settings: centralised multidisciplinary sarcoma units, neoadjuvant MAP, limb salvage in 80-90%, growing/expandable endoprostheses for skeletally immature children
• Limited-resource settings: later presentation with larger tumours and higher rates of pathological fracture, limited access to high-dose methotrexate monitoring, higher reliance on amputation and on biologic reconstruction (allograft, recycled autograft) where implants are unaffordable

High-Yield Take-Home Messages

1. Osteosarcoma = Most common primary bone cancer in adolescents, defined by osteoid production
2. Distal femur most common site (50%), "around the knee" in growing skeleton
3. Sunburst + Codman triangle on X-ray = osteosarcoma until proven otherwise
4. Biopsy MUST be planned with definitive surgeon - wrong approach contaminates compartments
5. MRI entire bone - skip lesions occur in 1-5%, change surgical planning
6. Neoadjuvant chemotherapy essential - MAP protocol (Methotrexate, Adriamycin, Platinum)
7. Histologic response is strongest prognostic factor - over 90% necrosis = good response
8. Limb salvage in 80-90% - equivalent survival to amputation
9. Parosteal = exception - low-grade surface tumor, wide resection alone, no chemo
10. Metastatic disease still aim for cure - complete resection of ALL disease improves survival

Common MCQ Scenarios