186 Re-1-hydroxyethylidene-1,1-diphosphonate (HEDP) is an attractive radiopharmaceutical for the treatment of bone pain arising from skeletal metastatic lesions. Currently, 186 Re-HEDP is most commonly used in European countries. The aim of this study was to investigate the palliative efficacy and adverse effects of 186 Re-HEDP in patients with different types of cancers and skeletal bone pain. Methods: Nineteen (8 male, 11 female) patients with various cancers (breast, prostate, renal cell carcinoma, colon, and neuroendocrine tumors) and painful bone metastases were included in the study. A dose of 1,480-3,330 MBq (40-90 mCi) of 186 Re-HEDP was administered intravenously. The patients' level of pain relief was assessed by the Visual Analog Scale for 8 wk after treatment and by a weekly blood cell count to evaluate for hematologic toxicity. Results: The overall response rate was 89.5%, and the mean pain score assessed by the Visual Analog Scale was reduced from 9.1 to 5.3 after 1 wk (P 5 0.003). No adverse effects were reported by patients during intravenous administration or for up to 24 h after administration. A flare reaction was seen in 63.2% of patients, mainly during days 1-3, and lasted for 2-4 d. There was no significant correlation between the response to therapy and the flare reactions (P . 0.05). The nadir of platelet reduction occurred at the fourth or fifth week and led to platelet infusion in only 4 patients with a low baseline platelet count and diffuse skeletal metastases. Bone marrow suppression occurred in patients receiving higher doses, but no clinical problems were seen except in 2 patients who required packed cell transfusion similar to their prior transfusions. Conclusion: 186 Re-HEDP is an effective radiopharmaceutical for the palliative treatment of metastatic bone pain and has minimal adverse effects.Key Words: rhenium 186(tin) etidronate; pain palliation; bone metastasis Nucl Med Technol 2013; 41:192-196 DOI: 10.2967/jnmt.113.124297 The skeleton is the most common site of metastatic disease, and tumors arising from the breast, prostate, lung, thyroid, and kidney commonly spread to bone. The frequency of bone metastases has been estimated at 65%-75% in patients with breast and prostate cancer (1,2) and about 30%-40% in those with lung cancer (3). Bone pain, as the main symptom of skeletal metastases and the most common type of cancer-related pain, obviously has a negative impact on quality of life (4). Currently, the factors contributing to cancer pain are not completely understood (5,6), and metastatic bone pain might be poorly localized for external radiation therapy (7). Various modalities have been introduced for the treatment of bone metastases, including analgesics, hormone therapy, cytotoxic drugs, biphosphonates, and surgery; however, they are not effective in all patients with painful refractory skeletal metastases. An alternative approach is systemic administration of radiopharmaceuticals, which is a valuable and effective method for relieving bone pain in patients with ...