Treatment of Metastatic Bone Disease and the Emerging Role of Radium-223

Bone metastases are common in advanced malignancy and, despite the developments in both anticancer and bone-targeted therapies in recent years, new therapeutic strategies are still needed. Traditionally, radioisotopes have been rarely used in part owing to concerns about bone marrow toxicity that limits retreatment and may prevent safe administration of subsequent chemotherapy. Radium-223 dichloride (Ra-223) is a calcium mimetic that binds preferentially to newly formed bone in areas of bone metastases, is the first alpha-emitting radionuclide to be developed for clinical use, and is approved for treatment of castration-resistant prostate cancer and symptomatic bone metastases. In this setting, it improves overall survival and delays symptomatic skeletal complications. The high linear energy transfer of the emitted alpha particles causes predominantly nonrepairable double-stranded deoxyribonucleic acid breaks in tumor cells, and the large size of the alpha particle, compared with other forms of radiation, results in a short path length and highly localized tissue destruction. As a result, Ra-223 has a highly favorable safety profile with a low level of myelosuppression. The role of Ra-223 in malignancy is discussed and the prospects for future development outlined.