Bone Metastasis – Causes, Symptoms and Treatment

What Are Bone Metastases?

Bone metastases (also called skeletal metastases) are secondary tumors that develop when cancer cells from a primary tumor – the original cancer site – travel through the bloodstream or lymphatic system and settle in bone tissue. They are not a primary bone cancer but rather a sign that an existing cancer has spread (metastasized). Bone metastases are a frequent complication of advanced cancer and can affect almost any bone, though they most commonly involve the spine, pelvis, ribs, skull, and long bones such as the femur and humerus.

Causes and Development

Bone metastases develop through a process called hematogenous or lymphogenous spread – cancer cells detach from the primary tumor, enter the bloodstream or lymphatic vessels, and are carried to bone tissue. Once there, they adhere to the bone surface, invade the tissue, and begin to multiply.

The most common primary cancers that cause bone metastases include:

• Breast cancer – most common cause in women
• Prostate cancer – most common cause in men
• Lung cancer
• Kidney cancer (renal cell carcinoma)
• Thyroid cancer
• Multiple myeloma (cancer of the bone marrow plasma cells)

Types of Bone Metastases

Based on their effect on bone tissue, there are two main types:

• Osteolytic metastases: The bone is broken down by cancer cells, creating cavities that weaken the bone and increase fracture risk. Typical of breast and lung cancer.
• Osteoblastic (osteosclerotic) metastases: Abnormal new bone formation occurs, making the bone denser but structurally unstable. Typical of prostate cancer.
• Mixed metastases: A combination of both bone destruction and abnormal new bone formation.

Symptoms

Bone metastases can cause a variety of symptoms depending on their location, number, and size. Some metastases remain asymptomatic for a long time. Common symptoms include:

• Bone pain: Often the first and most common symptom. The pain is typically dull, persistent, and worsens at night or with physical activity.
• Pathological fractures: Bone breaks that occur with minimal force because the bone has been weakened.
• Spinal cord compression: Metastases in the spine can press on the spinal cord, causing weakness, numbness, or loss of bladder and bowel control.
• Hypercalcemia: Elevated calcium levels in the blood due to bone breakdown, which can cause nausea, confusion, fatigue, and heart rhythm disturbances.
• Reduced mobility and general weakness in the affected area.

Diagnosis

Several imaging and laboratory methods are used to diagnose bone metastases:

• Bone scintigraphy (bone scan): A nuclear medicine technique that detects metabolic changes in bone early, often before structural changes are visible.
• X-ray: Shows advanced bone changes but may miss early metastases.
• Computed tomography (CT): Provides detailed cross-sectional images of the bone and surrounding structures.
• Magnetic resonance imaging (MRI): Particularly sensitive for detecting changes in bone marrow and soft tissue involvement.
• Positron emission tomography (PET-CT): Combines metabolic activity imaging with structural detail, highly accurate for staging.
• Blood tests: Elevated calcium, alkaline phosphatase, and tumor-specific markers can provide diagnostic clues.
• Biopsy: Tissue sampling for histological confirmation when the origin of the metastasis is unclear.

Treatment

Treatment of bone metastases is generally not curative. The main goals are: pain relief, preservation of bone integrity, prevention of complications, and improvement of quality of life. The treatment approach depends on the primary cancer type, the number and location of metastases, and the overall condition of the patient.

Systemic Therapies

• Chemotherapy: Targets the primary tumor and its metastases throughout the body.
• Hormone therapy: Used for hormone-sensitive tumors such as breast or prostate cancer.
• Targeted therapy: Drugs that attack specific molecular targets on cancer cells.
• Immunotherapy: Activates the body's immune system to fight the tumor.

Bone-Specific Therapies

• Bisphosphonates (e.g., zoledronic acid): Inhibit bone breakdown, reduce fracture risk, and relieve pain.
• Denosumab: A monoclonal antibody that inhibits bone resorption by blocking the RANKL signaling pathway.
• Radiation therapy: Highly effective for pain relief in localized metastases. Systemic radionuclide therapy (e.g., Radium-223) is an option for widespread bone involvement.

Surgical Interventions

• Stabilization of weakened or fractured bones using implants, intramedullary nails, or prostheses.
• Vertebral augmentation procedures (vertebroplasty or kyphoplasty) for spinal metastases.

Pain Management

Tailored pain management following the WHO analgesic ladder is a central component of treatment. This includes non-opioid analgesics, opioids for more severe pain, and adjuvant medications such as corticosteroids or anticonvulsants for neuropathic pain.

Prognosis

The prognosis for patients with bone metastases depends significantly on the primary tumor type, the extent of metastatic spread, and available treatment options. While bone metastases are generally not curable, modern therapies can meaningfully extend survival and substantially improve quality of life. Patients with breast or prostate cancer often have a more favorable outlook than those with lung or kidney cancer.

References

1. Coleman RE. – Skeletal complications of malignancy. Cancer. 1997;80(8 Suppl):1588–1594. PubMed PMID: 9362426.
2. Roodman GD. – Mechanisms of bone metastasis. New England Journal of Medicine. 2004;350(16):1655–1664. PubMed PMID: 15084698.
3. Macedo F, Ladeira K, Pinho F, et al. – Bone Metastases: An Overview. Oncology Reviews. 2017;11(1):321. PubMed PMID: 28584570.