Orthopedic Sarcomas — Comprehensive Overview

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EPIDEMIOLOGY AT A GLANCE

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PART I: SKELETAL (BONE) SARCOMAS

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1. OSTEOSARCOMA (Osteogenic Sarcoma)

Definition

Epidemiology

• Bimodal age distribution: 75% occur in patients <20 years (adolescent growth spurt); a second, smaller peak occurs in older adults with predisposing conditions
• Male:Female ratio: 1.6:1
• Secondary osteosarcomas arise in the context of Paget disease, prior radiation, bone infarcts

Location

• Metaphysis of long bones (near the growth plate)
• ~50% involve the distal femur or proximal tibia (around the knee)
• Rarely involves hands/feet

Pathogenesis — Molecular

No characteristic fusion gene (unlike Ewing sarcoma)

Radiology

• Mixed lytic and sclerotic destructive mass with infiltrative margins
• Codman triangle: reactive periosteal bone when periosteum is lifted — indicates aggressive tumor (not pathognomonic)
• Sunburst pattern: perpendicular spicules of tumor bone extending into soft tissue
• Breaks through cortex into soft tissues

Pathology (Morphology)

• Gross: bulky, gritty, tan-white tumor; areas of hemorrhage; cortical destruction; soft tissue invasion
• Histology: pleomorphic cells, large hyperchromatic nuclei, bizarre giant cells, numerous mitoses; lacelike osteoid produced by malignant cells is diagnostic
• Extensive necrosis and intravascular invasion are common

Types of Osteosarcoma

Clinical Features

• Painful, progressively enlarging mass
• Pathologic fracture may be first sign
• Local warmth, tenderness, swelling

Staging — Enneking System (MSTS)

• Stage I (low grade): Ia — intracompartmental; Ib — extracompartmental
• Stage II (high grade): IIa — intracompartmental; IIb — extracompartmental
• Stage III — any grade with metastases

Treatment

1. Neoadjuvant chemotherapy (MAP protocol: methotrexate, adriamycin/doxorubicin, cisplatin) — 3 cycles before surgery
2. Wide surgical resection (limb salvage in ~90% of cases; local recurrence target <7%)
3. Adjuvant chemotherapy post-surgery
4. Chemotherapy response assessed histologically — ≥90% necrosis = good response (Huvos Grade III/IV)

Limb salvage vs. amputation: Early studies by Simon and Link showed equivalent local recurrence and survival for distal femoral osteosarcoma.

Reconstruction Options

• Osteoarticular allograft
• Intercalary allograft
• Megaprosthesis (endoprosthesis) — modular metal implant; 10-year survival 50–80%
• Rotational flaps (e.g., medial gastrocnemius flap for proximal tibial tumors)

Prognosis

• 5-year survival: ~70% without overt metastases at diagnosis
• With clinically evident metastases or secondary osteosarcoma: <20% 5-year survival
• Metastasizes hematogenously: lungs (most common) > bone > brain

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2. EWING SARCOMA

Definition

Epidemiology

• Second most common primary bone sarcoma in children
• ~10% of primary malignant bone tumors
• 80% of patients are <20 years old; slight male predominance
• ~200 cases/year in the United States
• Rare in Black patients (genetic/ethnic predisposition)

Location

• Diaphysis of long bones (femur > tibia > fibula > humerus)
• Flat bones: pelvis, ribs, vertebrae
• 20% are extraskeletal (soft tissue Ewing sarcoma)

Pathogenesis — Molecular

• t(11;22)(q24;q12) in ~85% of cases → EWS–FLI1 fusion protein
• Remaining 15%: variant translocations (EWS-ERG, EWS-ETV1, EWS-FEV)
• EWS/FLI1 chimeric protein binds chromatin → dysregulates transcription → uncontrolled proliferation
• Cell of origin: likely mesenchymal stem cells or primitive neuroectodermal cells

All Ewing sarcoma family tumors (ESFT), including PNET and Askin tumor (chest wall), share the same translocation — they are considered the same entity.

Radiology

• Diaphyseal, permeative lytic lesion with ill-defined margins
• "Onion skin" periosteal reaction — concentric layers of reactive bone (classic)
• Large associated soft tissue mass
• May have aggressive sunburst pattern

Pathology (Morphology)

• Gross: soft, tan-white; hemorrhage and necrosis common; diaphyseal medullary origin with cortical and periosteal invasion
• Histology: sheets of uniform small round cells, slightly larger than lymphocytes, scant clear glycogen-rich cytoplasm
• Homer-Wright rosettes (cells arrayed around central fibrillary core) may be present
• No osteoid or cartilage production
• IHC: CD99 (MIC2) positive (diffuse membranous), FLI1 positive

Differential for small round blue cell tumors (SRBCT): Ewing sarcoma, neuroblastoma, rhabdomyosarcoma, lymphoma, small cell osteosarcoma — use IHC and molecular testing to distinguish.

Clinical Features

• Painful, enlarging mass at the diaphysis
• Affected site is tender, warm, and swollen (can mimic osteomyelitis — both may have fever, elevated ESR/CRP/WBC)
• Systemic symptoms (fever, weight loss) more common than in osteosarcoma

Treatment

• Systemic chemotherapy first (Ewing is considered a systemic disease from the outset)
• Standard regimen: VDC/IE (vincristine + doxorubicin + cyclophosphamide alternating with ifosfamide + etoposide) — typically 6 cycles before and after local treatment
• Local therapy: surgery, radiation, or both — choice depends on location and tumor factors
• Radiation is particularly useful for unresectable tumors (spine, sacrum, pelvis)

Prognosis

• With modern treatment: 75% 5-year survival; 50% long-term cure for non-metastatic disease
• Metastases at presentation → poor prognosis (<30% long-term survival)
• Chemotherapy response (% necrosis) is a key prognostic factor

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3. CHONDROSARCOMA

Definition

Epidemiology

• Most common primary bone cancer in adults (40% of adult bone sarcomas)
• Peak age: 40–60 years; men affected 2× more than women
• ~15% are secondary (arising from enchondroma or osteochondroma)

Location

• Axial skeleton predilection: pelvis (most common), shoulder girdle, ribs
• Unlike osteosarcoma, which favors the metaphysis of long bones
• When peripheral: proximal long bones (femur, humerus)

Classification

Pathogenesis — Molecular

• Arising in multiple hereditary exostosis: loss-of-function mutations in EXT1/EXT2 (regulate cartilaginous matrix protein synthesis)
• Sporadic and exostosis-related: IDH1 or IDH2 mutations (also seen in glioma, AML)
• CDKN2A silencing by DNA methylation common in sporadic tumors

Radiology

• Destroys cortex and may form a soft tissue mass
• "Popcorn" / "rings and arcs" calcifications — characteristic of chondroid matrix
• "Endosteal scalloping" (>2/3 width of cortex in enchondroma = worrisome for chondrosarcoma)
• On MRI: hyperintense on T2 (high water content of cartilaginous matrix); lobular architecture

Pathology (Morphology)

• Gross: bulky nodules of glistening gray-white translucent cartilage; gelatinous myxoid areas; focal calcifications; possible central necrosis
• Histology: cartilage infiltrates the marrow space, entrapping normal trabeculae
• Grading (correlates with prognosis):
  • Grade 1: low cellularity, plump vesicular nuclei, small nucleoli
  • Grade 2: increased cellularity, mild-moderate atypia
  • Grade 3: high cellularity, extreme pleomorphism, bizarre giant cells, frequent mitoses

Clinical Features

• Painful, progressively enlarging mass
• Symptoms may be present for months to years before diagnosis (especially low-grade)
• Pathologic fracture may occur

Treatment

• Wide surgical excision is the definitive treatment
• Chemotherapy and radiation are NOT effective for conventional chondrosarcoma — this is a key distinguishing feature
• Pelvic chondrosarcomas often require hemipelvectomy or internal hemipelvectomy with complex reconstruction (megaprosthesis, 3D-printed implants)

Prognosis

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4. CHORDOMA

• Arises from notochordal remnants — skull base (clivus) and sacrococcygeal region
• Slow-growing, locally destructive; not truly a sarcoma but classified with bone tumors
• IHC: Brachyury positive (pathognomonic), S-100 positive, cytokeratin positive
• Treatment: wide resection; proton beam radiation for skull base lesions
• 10% of primary bone cancers in adults

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PART II: SOFT TISSUE SARCOMAS (STS)

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General Features of All Soft Tissue Sarcomas

Epidemiology

• ~70 distinct histologic subtypes arising from any anatomic site
• Tissues of origin: skeletal muscle, adipose, blood/lymphatic vessels, other mesoderm, peripheral nerves (neuroectoderm)
• ~13,400 new cases/year in the USA; ~5,140 deaths/year → 1% of cancer incidence
• Most common site: thigh (44% of extremity STSs); proximal limb > distal
• Majority arise sporadically

Genetic Syndromes Predisposing to STS

General Principles — Diagnosis

• STS present as painless enlarging masses >5 cm (pain is possible)
• Any deep mass >5 cm warrants biopsy
• MRI is the gold standard for local staging
• CT chest for pulmonary metastasis staging
• Biopsy should be performed at a sarcoma center — biopsy-related complications and changes in outcome are significantly lower when done at specialized centers

General Principles — Staging (AJCC/Enneking)

• Stage I — low grade (Ia: intracompartmental; Ib: extracompartmental)
• Stage II — high grade (IIa: intracompartmental; IIb: extracompartmental)
• Stage III — any grade with regional/distant metastases

Metastatic Pattern

• Lung = most common site of STS metastasis (hematogenous)
• Lymph node metastasis is rare (~5%) — except in specific subtypes: E-S-A-R-C mnemonic:
  • Epithelioid sarcoma (most common STS of the hand, young adults)
  • Synovial sarcoma
  • Angiosarcoma
  • Rhabdomyosarcoma
  • Clear cell sarcoma

General Treatment Principles

1. Wide surgical resection (goal: negative margins)
2. Radiation — adjuvant for high-grade, large tumors (reduces local recurrence)
3. Chemotherapy — doxorubicin ± ifosfamide as first-line for advanced/metastatic disease

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Major STS Subtypes

1. Undifferentiated Pleomorphic Sarcoma (UPS)

• Most common STS in adults >40 years
• Deep soft tissues of extremities
• Histology: spindle and histiocytic cells arranged in storiform (cartwheel) pattern; slit-like vessels; chronic inflammatory cells
• High grade; frequent recurrence and metastasis

2. Liposarcoma

• Most common STS in adults overall (or UPS — varies by series)
• Rarely in subcutaneous tissue; typically deep retroperitoneum or thigh
• IHC: MDM2 positive (especially well-differentiated/dedifferentiated)
• Histology: lipoblasts (signet ring-shaped cells) are hallmark
• Subtypes:

  Subtype	Grade	Features
  Well-differentiated (WDLPS)	Low	MDM2/CDK4 amplification
  Dedifferentiated (DDLPS)	High	WDLPS + high-grade spindle cell component
  Myxoid	Low–intermediate	t(12;16) → FUS-DDIT3 fusion
  Round cell	High	High-grade variant of myxoid
  Pleomorphic	High	Rare; worst prognosis

3. Leiomyosarcoma

• Arises from smooth muscle (uterus, retroperitoneum, blood vessel walls)
• Histology: fascicular growth with spindle cells intersecting at right angles ("herringbone" variant)
• IHC: smooth muscle actin (SMA) and desmin positive
• Treatment: surgical resection; gemcitabine + docetaxel for metastatic disease

4. Rhabdomyosarcoma (RMS)

• Most common STS in children
• Occurs in young adults as well
• Subtypes: embryonal (most common, best prognosis), alveolar (t(2;13) → PAX3-FOXO1 or t(1;13) → PAX7-FOXO1), pleomorphic (rare, adults)
• IHC: myogenin, MyoD1, desmin positive
• Treatment: multimodality (chemotherapy + surgery ± radiation); VAC regimen
• Lymph node metastasis common (ESARC)

5. Synovial Sarcoma

• Misnomer — does not arise from synovium; likely from pluripotent mesenchymal cells
• Common in young adults; para-articular location (near joints, especially knee)
• t(X;18) → SYT-SSX1 or SYT-SSX2 fusion products (2 most common)
• Histology: biphasic (epithelial + spindle cell) or monophasic
• IHC: TLE1 positive, cytokeratin positive, EMA positive
• Lymph node metastasis possible (ESARC)
• Treatment: surgery + radiation ± chemotherapy (ifosfamide-sensitive)

6. Angiosarcoma

• Resembles endothelium of blood vessels
• Highly malignant — worst prognosis among STS
• Stewart-Treves syndrome: angiosarcoma arising in chronic lymphedematous arm (post-mastectomy)
• Cutaneous and lymph node metastases common
• Infiltrative with poor margins — amputation may be necessary
• IHC: CD31, CD34, ERG positive

7. Malignant Peripheral Nerve Sheath Tumor (MPNST)

• Arises de novo or in neurofibromatosis type 1 (NF1)
• NF1 patients have 10% lifetime risk of MPNST
• Histology: spindle cells in sweeping fascicles with nodular/whorled areas
• IHC: S-100 positive (often focal)
• High grade; poor prognosis

8. Epithelioid Sarcoma

• Young adults; most common STS of the hand/wrist
• Two types: classical (distal) and proximal (more aggressive)
• IHC: cytokeratin positive, EMA positive, INI1 (SMARCB1) lost
• Lymph node metastasis common (ESARC)

9. Clear Cell Sarcoma

• Young adults; common in lower extremity/foot (attached to tendons and aponeuroses)
• t(12;22) → EWS-ATF1 fusion
• IHC: S-100 and HMB-45 positive (melanocytic markers)
• Lymph node metastasis (ESARC)

10. Fibrosarcoma

• Histology: fasciculated spindle cells with scanty cytoplasm separated by interwoven collagen — "herringbone" pattern (intersecting fascicles with transverse vs. longitudinal nuclei in adjacent fascicles)
• Can arise de novo or from radiation

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PART III: BONE MICROENVIRONMENT & SARCOMA BIOLOGY

• RANKL / RANK axis: RANKL (produced by osteoblasts) binds RANK on osteoclast precursors → stimulates osteoclastogenesis. Tumor cells exploit this "vicious cycle" to promote bone destruction.
• CXCL12 / CXCR4 axis: mesenchymal stem cells secrete CXCL12; circulating tumor cells (e.g., breast cancer) express CXCR4 → homing to marrow
• Denosumab (anti-RANKL monoclonal antibody): used in giant cell tumor of bone and bone metastases

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DIAGNOSTIC APPROACH SUMMARY

Step 1: History & Exam
  Age → helps narrow differential (age-specific tumor chart)
  Pain characteristics (night pain, at rest = more aggressive)
  Personal history: cancer, radiation, genetic syndromes
  Physical: mass size, depth, lymph nodes, café-au-lait spots (NF1)

Step 2: Labs
  CBC, ESR, CRP, LDH (elevated in Ewing), ALP (elevated in osteosarcoma)
  PSA (if metastatic disease suspected in older male)

Step 3: Imaging
  Plain X-ray FIRST (location, matrix, periosteal reaction, zone of transition)
  MRI (gold standard for local staging and soft tissue sarcomas)
  CT chest (lung metastases)
  Bone scan or PET (skip lesions, multifocal disease)

Step 4: Biopsy
  MUST be performed at sarcoma center (specialist placement critical)
  Core needle biopsy preferred
  Biopsy tract must be excised en bloc with specimen at definitive surgery
  Gene fusion testing (molecular) where applicable

Step 5: Staging (Enneking/AJCC)
  Grade + compartment + metastases

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QUICK COMPARISON TABLE

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STAGING: ENNEKING / MSTS SYSTEM (Applicable to All Bone & STS)

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What Was Covered

1. Osteosarcoma — most common in adolescents; metaphyseal; Codman triangle / sunburst on X-ray; RB/TP53 mutations; treated with MAP chemotherapy + wide resection; 70% 5-year survival
2. Ewing Sarcoma — diaphyseal; <20 yrs; t(11;22) EWS-FLI1; "onion-skin" periosteal reaction; small round blue cells; treated with VDC/IE chemotherapy ± surgery/radiation; 75% survival
3. Chondrosarcoma — most common adult bone sarcoma; axial/pelvis; "popcorn" calcification; IDH1/2 mutations; chemo/radiation-resistant — surgery only; grade-dependent prognosis
4. Chordoma — notochordal origin; Brachyury+; sacrum/clivus

• Enneking staging system (Stage I–III)
• Diagnostic approach (imaging → biopsy protocol)
• ESARC mnemonic for STSs with lymph node metastases
• Bone microenvironment and RANKL biology

Orthopedic Sarcomas — Summary Comparison

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🦴 BONE SARCOMAS — Master Comparison Table

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🧬 GENETIC / MOLECULAR SNAPSHOT

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🔬 SOFT TISSUE SARCOMAS — Subtype Snapshot

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🏥 LYMPH NODE METASTASIS — ESARC Mnemonic

Most STS spread to lungs (not lymph nodes). Only 5% spread to lymph nodes — but these 5 types do:

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📊 ENNEKING STAGING — All Bone & STS

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⚡ ONE-LINE MEMORY HOOKS

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