Samarium Sm-153 lexidronam for the palliation of bone pain associated with metastases

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Abstract
In patients with bone pain due to metastatic disease, intravenous systemic radioisotope therapy may be a useful adjunct to other methods for palliating pain. Various studies have been performed utilizing a short-lived radioisotope conjugated to a tetraphosphonate (samarium 153 lexidronam) both as an open label and as a double blinded, placebo-controlled study. Patients with varying tumor types including those of the prostate, breast, lung, and other sites were studied. Two dose levels were used (0.5 millicuries (mCi)/kg and 1.0 mCi/kg) with patients monitored for 16 weeks for efficacy (pain scores, opiod analgesic score, and quality of life) parameters and adverse events. All 3 studies showed that at the 1.0 mCi/kg dose level statistically significant improvement over placebo was observed by 4 weeks with relief of pain noted in many patients by 1 week. The only significant adverse event was transient myelosuppression with a nadir at 4-6 weeks and recovery by 8 weeks. Less than 10% of patients had National Cancer Institute Common Toxicity Criteria Grade III/IV bone marrow toxicity recorded. Systemic metabolic radiotherapy with samarium 153 lexidronam appears to be a safe and efficacious method for treating patients with bone pain. The shorter radioisotope half-life allows for a high dose rate to be delivered over a short period, which may have certain biologic benefits.