Metastatic Bone Disease

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Overview & Primaries - Cancer's Bony Outposts

  • Definition: Secondary tumor deposits in bone from a distant primary malignancy. Most common bone tumors in adults.
  • Common Adult Primaries (Mnemonic 📌 PB KTL):
    • Prostate cancer
    • Breast cancer
    • Kidney (Renal Cell Ca)
    • Thyroid cancer
    • Lung cancer
    • Myeloma (primary marrow cancer, presents with bone lesions).

⭐ Most common primary cancer metastasizing to bone in adult males is Prostate cancer; in adult females is Breast cancer.

  • Commonest Primary in Children: Neuroblastoma.
  • Skeletal Predilection: Axial skeleton (vertebrae, pelvis, ribs, skull) & proximal long bones; due to abundant red marrow (hematogenous spread). Skeletal distribution of metastatic tumors

Pathophysiology & Patterns - How Tumors Invade

  • Mechanisms of Tumor Spread:
    • Hematogenous: Most common; Batson's plexus of veins (valveless) facilitates vertebral metastases.
    • Lymphatic spread.
    • Direct extension from adjacent tumor.
  • Patterns of Bone Involvement:
    • Osteolytic (bone destruction): Lung, Kidney, Thyroid, Multiple Myeloma. Mediated by ↑osteoclast activity (e.g., RANKL, PTHrP).
    • Osteoblastic (bone formation): Prostate, Carcinoid. Mediated by ↑osteoblast activity (e.g., Endothelin-1).
    • Mixed patterns: Breast, GI tumors.
  • Key Molecular Players: RANKL, OPG (Osteoprotegerin), PTHrP (Parathyroid Hormone-related Protein), DKK-1 (Dickkopf-1), Endothelin-1.
  • Commonest Skeletal Sites: Vertebrae (>50%), Pelvis, Ribs, Femur (proximal), Humerus (proximal). (📌 "Very Painful Ribs Feel Horrible")

Tumor-bone cell interactions in metastatic bone disease

⭐ Osteolytic lesions are predominantly mediated by osteoclast activation via the RANK-RANKL pathway, often stimulated by PTHrP.

Diagnosis & Staging - Spotting the Spread

  • Presentation: Bone pain (often nocturnal, mechanical, worse with activity), pathological fractures, hypercalcemia (nausea, confusion), spinal cord compression (neurological deficits, bladder/bowel dysfunction).
  • Labs: Sr. Calcium, Alkaline Phosphatase (Alk Phos), PSA (for prostate cancer), other relevant tumor markers.
  • Imaging: Metastatic Bone Disease: CT, PET-CT, and PET Imaging
    • X-ray: Initial; may show lytic (lucent), blastic (sclerotic), or mixed lesions; periosteal reaction.
    • Bone Scan (Tc-99m MDP): Detects ↑osteoblastic activity / bone turnover (hot spots).

    ⭐ Bone scan (Tc-99m MDP) is highly sensitive for osteoblastic metastases but can be falsely negative in purely lytic lesions (e.g., multiple myeloma, renal cell carcinoma); skeletal survey or PET-CT preferred then.

    • MRI: Best for marrow infiltration, soft tissue extension, spinal cord assessment (especially for compression).
    • PET-CT: Whole-body staging, assessing metabolic activity, and treatment response.
  • Biopsy Indications: Unknown primary tumor, solitary bone lesion (to rule out primary bone tumor), or if diagnosis is unclear after imaging.
  • Mirels' Scoring: For impending pathological fracture risk in long bones (Site, Pain, Lesion type [lytic/blastic/mixed], Size). Score >8 often indicates need for prophylactic fixation.
  • Diagnostic Flow:

Treatment & Complications - Fighting Back & Fallout

Goals: Pain relief, function, stability, local control, prevent fractures. Multidisciplinary.

Systemic Therapy:

  • Chemo, Hormonal, Targeted, Immunotherapy.
  • Bone-modifying: Zoledronic acid (4mg IV q3-4wks), Denosumab (120mg SC q4wks).

Local Therapy:

  • Radiotherapy (RT): EBRT for pain (8Gy x1, 20Gy x5, 30Gy x10), MSCC.
  • Surgery: Prophylactic fixation (Mirels' score), fracture stabilization, vertebroplasty.

Key Complications & Management:

  • Pathological fractures: Surgical fixation.
  • Spinal Cord Compression (MSCC): 🚨EMERGENCY!
  • Hypercalcemia: IV fluids, bisphosphonates.

⭐ For suspected MSCC, immediate high-dose corticosteroids (e.g., Dexamethasone) are crucial pending urgent MRI and definitive treatment.

High‑Yield Points - ⚡ Biggest Takeaways

  • Metastatic disease is the most common malignant bone tumor overall.
  • Common primaries: Prostate (blastic), Breast (mixed/lytic), Lung (lytic), Kidney (lytic), Thyroid (lytic) (PBLKT).
  • Axial skeleton (vertebrae, pelvis, ribs) is most frequently affected.
  • Clinical features: Severe bone pain (worse at night), pathological fractures, hypercalcemia.
  • Diagnosis: X-ray (lytic/blastic lesions), bone scan (sensitive for screening), biopsy (definitive).
  • Management is primarily palliative, focusing on pain relief and fracture prevention (radiotherapy, bisphosphonates).
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Practice Questions: Metastatic Bone Disease

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An elderly woman presented with confusion, thirst, and abdominal pain symptoms. On examination, she had pallor and thoracic spine tenderness. X-ray spine showed osteolytic lesions. Her lab investigations showed the following findings. What is the most likely diagnosis? - Hb - 6.9 g/dl

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Flashcards: Metastatic Bone Disease

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The bone lesions seen with multiple myeloma are most common in the _____ and skull

TAP TO REVEAL ANSWER

The bone lesions seen with multiple myeloma are most common in the _____ and skull

vertebrae

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