Bone Seeking Radiopharmaceuticals for Palliation of Pain in Cancer Patients with Osseous Metastases

Many patients with cancer develop symptomatic skeletal metastases at an advanced stage of their disease. Skeletal metastases are often complicated by pain. They cause considerable morbidity and mortality. Besides analgesics, treatment options include external beam radiotherapy, bisphosphonates, chemotherapy, surgery and bone seeking radiopharmaceuticals. Pain palliation with bone seeking radiopharmaceuticals has proved to be an effective treatment modality in patients with metastatic bone pain. Radiopharmaceuticals bind to the bone matrix in areas of increased bone turnover, due to a metastatic response. Beta rays from the specific radionuclide, bound to its carrier ligand, result in the therapeutic effect. Various radiopharmaceuticals have been developed for this purpose. All have their own characteristics. The radiopharmaceuticals Samarium-153-ethylenediaminetetramethylenephosphonic acid (153Sm-EDTMP) and Strontium- 89-Chloride, which are approved in the USA and Europe, as well as the not universally approved Rhenium-186-hydroxyethylidenediphosphonic acid (186Re-HEDP), will be discussed in greater detail. Depending on the half-life and radiation energy of the specific radionuclide, they exert a different effect and toxicity profile. In most cases, bone marrow toxicity is limited and reversible, which makes repetitive treatment relatively safe. Several studies have shown encouraging clinical results of palliative therapy using bone seeking radiopharmaceuticals, with an overall reported pain response rate in the order of ± 70-80% of patients. This systemic form of radionuclide therapy is simple to administer and complements other treatment options. It has been associated with marked pain reduction, improved mobility in many patients, reduced dependence on analgesics, and improved performance status and quality of life. Additionally, new therapeutic strategies hold the promise of enhancement of the palliative and anticancer effects of this form of therapy.