Bone Tumors and Tumor-like Lesions

Bone Tumor Basics - The Bony Blueprint

• Definition: Abnormal cell proliferation in bone.
• Classification:
  • Origin: Primary (from bone/cartilage cells) vs. Secondary (metastatic).
  • Behavior: Benign vs. Malignant.
  • Histogenesis: Bone-forming (e.g., Osteosarcoma), Cartilage-forming (e.g., Chondrosarcoma), Fibrous, Round cell (e.g., Ewing sarcoma), Giant cell tumors.
• Benign Signs: Well-defined, sclerotic rim, intact cortex, no soft tissue extension.
• Malignant Signs: Ill-defined, lytic/permeative pattern, cortical destruction, soft tissue mass, aggressive periosteal reactions (e.g., Codman triangle, sunburst).

⭐ Metastases are the most common malignant tumors found in bone overall in adults.

Benign Bone Buddies - Mostly Harmless

• Osteochondroma (Exostosis):

  • Most common benign. Age: < 20 yrs.
  • Site: Metaphysis (e.g., knee). Cartilage-capped bony spur.
  • Radiology: Points away from joint.
  • 
  • ⭐ > Malignant change to chondrosarcoma rare (< 1%), ↑ risk in multiple hereditary exostoses.

• Osteoid Osteoma:

  • Age: < 25 yrs (males).
  • Site: Cortex of long bones (femur, tibia).
  • Clinical: Nocturnal pain, relieved by NSAIDs.
  • Radiology: Small (< 1.5 cm) radiolucent nidus, dense sclerosis.

• Giant Cell Tumor (GCT):

  • Age: 20-40 yrs.
  • Site: Epiphysis (e.g., knee). Locally aggressive.
  • Radiology: "Soap bubble" lytic lesion.

• Enchondroma:

  • Age: 20-50 yrs.
  • Site: Medulla of small bones (hands/feet).
  • Radiology: Lytic, "rings & arcs" calcification.
  • 📌 Ollier disease (multiple), Maffucci syndrome (with hemangiomas, ↑ malignancy risk).

• Fibrous Dysplasia:

  • Developmental.
  • Radiology: "Ground-glass" opacity.
  • Histology: "Chinese letter" trabeculae (woven bone, no osteoblastic rimming).

Malignant Monsters - Serious Bone Breakers

• Osteosarcoma: Most common primary malignant bone tumor (excluding myeloma).
  • Age: 10-20 yrs (peak); also >65 yrs.
  • Site: Metaphysis of long bones (knee, proximal humerus).
  • X-ray: Codman triangle, sunburst appearance. Histo: Malignant osteoid production.
  • Genetics: Associated with RB1, TP53 (Li-Fraumeni syndrome).
• Chondrosarcoma: Malignant cartilage-forming tumor.
  • Age: 40-60 yrs.
  • Site: Axial skeleton (pelvis, ribs), proximal femur/humerus.
  • X-ray: Endosteal scalloping, ring-and-arc or "popcorn" calcification.
• Ewing Sarcoma: Aggressive small round blue cell tumor.
  • Age: 10-15 yrs.
  • Site: Diaphysis of long bones, pelvis, scapula.
  • X-ray: "Onion-skin" periosteal reaction, lytic lesions, moth-eaten appearance.
  • Genetics: t(11;22) EWS-FLI1 fusion. 📌 (Ewing Flew to 1122 street).
• Multiple Myeloma (Plasma Cell Myeloma): Most common primary malignant tumor of bone overall.
  • Age: >50 yrs (peak 65-70 yrs).
  • Site: Vertebrae, ribs, skull, pelvis (areas with hematopoietic marrow).
  • X-ray: "Punched-out" lytic lesions. Lab: M-spike (serum/urine protein electrophoresis).

⭐ Ewing Sarcoma is characterized by the t(11;22)(q24;q12) chromosomal translocation, resulting in the EWS-FLI1 fusion gene, crucial for diagnosis and a potential therapeutic target. This translocation is found in ~85% of cases.

Tumor Mimics & Workup - Looks Can Deceive

• Common Tumor Mimics:

  • Infection (Osteomyelitis, Brodie's abscess)
  • Fracture Callus
  • Fibrous Dysplasia
  • Myositis Ossificans
  • Brown Tumor (Hyperparathyroidism)
  • Langerhans Cell Histiocytosis (Eosinophilic Granuloma)
  • Paget's Disease (lytic/sclerotic phases)

• Diagnostic Pathway:

⭐ Biopsy tract must be planned for en-bloc resection with the tumor during definitive surgery to prevent local recurrence.

• Staging: Enneking (Benign S1-S3; Malignant G, T, M), AJCC TNM for sarcomas.

High‑Yield Points - ⚡ Biggest Takeaways

• Osteosarcoma: Most common primary malignant bone tumor, typically around the knee; Codman triangle, sunburst pattern.
• Ewing Sarcoma: Small round blue cell tumor; t(11;22) translocation; onion-skin periosteal reaction.
• Giant Cell Tumor: Epiphyseal location in adults; soap-bubble appearance on X-ray; locally aggressive.
• Osteochondroma: Most common benign bone tumor; cartilage-capped bony projection (exostosis).
• Chondrosarcoma: Malignant cartilage-forming tumor in older adults; commonly affects pelvis, ribs, femur.
• Metastases: Most common overall malignant tumors OF bone (secondary to other cancers like breast, lung, prostate).
• Fibrous Dysplasia: Benign lesion; ground-glass appearance; associated with McCune-Albright syndrome (polyostotic form).