Skeletal metastases are commonly encountered in cancer patients and often result in great pain and morbidity (1). Autopsy studies have shown that in patients who die from breast, prostate and lung cancer, up to 85% have evidence of bone metastasis at the time of death (2). Severe pain and frequent fractures resulting from metastatic cancer reduce the patients' quality of life and often lead to depression and mood changes.

The current standard of care for cancer patients with localized bone pain is external beam radiation therapy (RT). While most patients experience a reduction of pain, 20% to 30% of patients do not have relief. A recent review of 1,016 patients treated by RT demonstrated complete relief in 53% and partial relief in 83% (3). Additionally, following treatment, there is usually a delay of 4 to 12 weeks before pain relief is achieved, and many patients will experience a return of significant pain within a few months (3). Other conventional therapies have specific, although limited, usefulness for treating painful metastatic disease. Surgery is usually reserved for fixation of a recent or impending fracture. Chemotherapy is usually ineffective for reduction of bone pain, although bisphosphonate therapy is useful for metastatic breast and prostate cancers (4–7). Radiopharmaceuticals may be of value for treatment of some patients with diffuse bone metastases but is not used for patients with focal painful metastatic disease (8–10).