Malignant Primary Bone Tumors

Malignant Bone Tumors - Skeletal Red Alerts

Primary malignant bone tumors are cancerous growths originating within bone tissue. Red Flags: Persistent pain (worse at night), localized swelling, palpable mass, unexplained pathological fracture.

• General Classification:

  • Osteogenic (e.g., Osteosarcoma)
  • Chondrogenic (e.g., Chondrosarcoma)
  • Hematopoietic (e.g., Myeloma, Lymphoma)
  • Fibrogenic/Histiocytic
  • Small Round Cell Tumors (e.g., Ewing's Sarcoma)

• Initial Diagnostic Steps:

  • X-ray: First-line imaging.
  • MRI: Evaluates tumor extent, soft tissue involvement.
  • Biopsy: Essential for histological diagnosis and grading.

⭐ Most primary malignant bone tumors, like osteosarcoma, commonly metastasize to the lungs.

Osteosarcoma - Sunburst Menace

• Most common primary malignant bone tumor (excl. myeloma). 📌 Osteo-SUN-coma (SUNburst).
• Epi: Bimodal: adolescents (10-20 yrs); elderly (>65 yrs, often 2° to Paget's disease).
• Sites: Metaphysis of long bones; ~50% around knee (distal femur, prox. tibia, prox. humerus).
• X-ray:
  • Sunburst appearance (tumor spicules).
  • Codman's triangle (periosteal elevation).
  • Lytic, sclerotic, or mixed lesions.
  • Periosteal reaction (new bone).
• Histo: Malignant osteoid production by tumor cells.
• Genetics: RB1, TP53 (Li-Fraumeni syndrome), MDM2.
• Labs: ↑ Serum Alkaline Phosphatase (ALP), ↑ LDH.
• Rx: Neoadjuvant chemotherapy → surgical resection (wide) → adjuvant chemotherapy.

⭐ Prognosis significantly depends on response to neoadjuvant chemotherapy (e.g., Huvos grading; >90% tumor necrosis is a good prognostic factor).

Ewing Sarcoma - Onion Skin Bully

• Epidemiology: Second most common malignant bone tumor in children/young adults.
• Site: Diaphysis of long bones (femur, tibia, humerus), pelvis, ribs.
• X-ray:
  • Lytic lesion.
  • 'Onion-peel' periosteal reaction (classic).
  • 'Moth-eaten' appearance.
  • Codman's triangle (possible).
• Histopathology:
  • Small, round, blue cells.
  • Homer-Wright rosettes (neuroectodermal differentiation).
  • PAS positive (glycogen granules).
• Genetics:
  • Characteristic translocation $t(\mathbf{11};\mathbf{22})(q24;q12)$ → EWS-FLI1 fusion protein. 📌 EWIng = Eleven + Twenty-two.
  • CD99 positive.
• Clinical: Systemic symptoms (fever, weight loss, anemia, ↑ESR).
• Treatment: Highly chemosensitive & radiosensitive. Multimodal: chemotherapy, surgery, +/- radiotherapy.

⭐ Exam Favourite: The $t(\mathbf{11};\mathbf{22})$ translocation leading to the EWS-FLI1 fusion protein is pathognomonic for Ewing Sarcoma and a key diagnostic marker.

Chondrosarcoma - Popcorn Peril

• Malignant tumor of cartilage-producing cells.

• Age: Typically older adults, >40 years.

• Sites: Common in pelvis, proximal femur, ribs, humerus. Can arise de novo or secondary to benign lesions (osteochondroma, enchondroma).

• X-ray: Lytic lesion with characteristic 'popcorn', 'ring-and-arc', or 'punctate' calcification; endosteal scalloping; cortical thickening/destruction.

• Clinical: Often slow-growing, presenting with pain and swelling.

• Histology: Malignant chondrocytes within lacunae, variable grades (1-3).

• Treatment: Primarily surgical (wide local excision).

⭐ Low-grade chondrosarcomas are notably resistant to chemotherapy and radiotherapy.

High‑Yield Points - ⚡ Biggest Takeaways

• Osteosarcoma: Most common primary (excl. myeloma); metaphysis (knee); Codman's triangle, sunburst appearance.
• Ewing's Sarcoma: t(11;22), small round blue cells; diaphysis; onion-peel periosteal reaction.
• Chondrosarcoma: Adult cartilage malignancy; pelvis, femur; X-ray: rings & arcs, popcorn calcification.
• Multiple Myeloma: Most common primary overall; plasma cell origin; punched-out lytic lesions, Bence Jones protein.
• Adamantinoma: Rare, low-grade; anterior tibia commonest; X-ray: soap bubble appearance.
• Chordoma: From notochordal remnants; sacrum & clivus typical; physaliphorous cells.