Metastatic Bone Disease

Mets to Bones - Unwelcome Guests

• Most common malignant bone tumors; significantly outnumber primary bone sarcomas.
• Axial skeleton favored: Vertebrae, pelvis, ribs, skull, proximal femur/humerus.
• Common Primaries (📌 "PB KTL"): Prostate, Breast, Kidney, Thyroid, Lung.
  • Osteoblastic: Prostate (classic), some Breast.
  • Osteolytic: Lung, Kidney, Thyroid, Myeloma.
  • Mixed: Breast.
• Symptoms: Bone pain (often nocturnal, progressive), pathological fractures, hypercalcemia, neurological deficits (e.g., cord compression).

⭐ Lung, breast, and prostate cancers account for approximately 80% of all skeletal metastases.

Bone Under Siege - Lytic vs Blastic

• Pathogenesis: Tumor cells secrete factors (cytokines, growth factors) altering bone remodeling.
• Lytic Lesions (Osteolytic): "Bone breaking"
  • Mechanism: ↑ Osteoclast activity (e.g., PTHrP, RANKL).
  • Radiology: Radiolucent, "punched-out" defects.
  • Primaries: Multiple Myeloma, Lung, Kidney, Thyroid, Breast (lytic or mixed).
• Blastic Lesions (Osteosclerotic): "Bone forming"
  • Mechanism: ↑ Osteoblast stimulation (e.g., Endothelin-1).
  • Radiology: Radiodense, sclerotic bone.
  • Primaries: Prostate (classic), Breast (mixed or blastic), Carcinoid.
• Mixed Pattern: Common in Breast, Lung.

and blastic (white areas) bone metastases)

⭐ Prostate cancer is notorious for causing osteoblastic metastases, while Multiple Myeloma typically causes purely lytic lesions.

Red Flags Waving - Signs & Scans

• Clinical Alarms:
  • Persistent bone pain (nocturnal/rest pain ↑).
  • Pathological fractures (minimal trauma).
  • Neurological deficits (spinal cord compression).
  • Hypercalcemia symptoms (confusion, constipation).
  • Known primary cancer history.
• Imaging Arsenal:
  • X-ray: Initial; lytic (e.g., lung, kidney), blastic (e.g., prostate), mixed lesions.
  • Bone Scan (Tc-99m): Sensitive for blastic activity; multiple lesions.
  • MRI: Marrow, soft tissue, cord compression.
  • CT: Bone detail, biopsy guidance.
  • PET-CT: Lytic lesions, staging, response.

⭐ Most common primary cancers metastasizing to bone: Prostate, Breast, Lung, Kidney, Thyroid. (📌 PB-KTL: "Painful Bones Kill Teens Like")

Risk Rating - Scores & Survival

• Mirel's Score: Predicts pathological fracture risk in long bones.
  • Factors: Site, Pain, Lesion type (lytic/blastic), Size of lesion.
  • Score ≥ 9: Prophylactic fixation recommended.
  • Score ≤ 7: Non-operative management.
• Tokuhashi Score (Revised): Estimates survival for spinal metastases.
  • Factors: KPS, extraspinal mets, vertebral mets, visceral mets, primary cancer, palsy.
  • Score 0-8: Poor prognosis (< 6 months survival).
  • Score 12-15: Better prognosis (> 12 months survival).

⭐ A Mirel's score of 8 is considered borderline, requiring individualized decision for fixation.

The Counterattack - Treatment Toolkit

Goals: Palliation, prevent/treat fractures (SREs), local control. Multimodal approach.

• Systemic Therapy:
  • Bone-Targeted Agents: Bisphosphonates (e.g., Zoledronate), Denosumab (↓SREs).
  • Primary-Specific: Chemo, Hormonal, Targeted Rx.
• Local Therapy:
  • Radiotherapy (RT): EBRT for pain (8 Gy single; 20 Gy/5fr; 30 Gy/10fr), local control.
  • Surgery: Pathological/impending # (Mirels score >8), spinal cord compression, instability, solitary lesion.
    • Procedures: Internal fixation, arthroplasty, excision.
• Supportive Care:
  • Analgesia (WHO ladder), Rehabilitation.

⭐ For painful bone metastases, a single 8 Gy fraction of radiotherapy offers pain relief comparable to multifraction regimens with greater convenience.

High‑Yield Points - ⚡ Biggest Takeaways

• Most common primary cancers to bone: Prostate, Breast, Lung, Kidney, Thyroid (PB KTL).
• Spine is the most frequent metastatic site, followed by pelvis and femur.
• Pain (often nocturnal) and pathological fractures are key clinical features.
• Lesions: Osteolytic (e.g., Lung, Kidney), Osteoblastic (e.g., Prostate), or Mixed (e.g., Breast).
• Bone scan for screening; biopsy for definitive diagnosis. X-ray is initial imaging.
• Management: Multimodal-radiotherapy for pain, bisphosphonates, surgical stabilization for fractures.
• Mirels' score assesses impending fracture risk in long bones_