Bone pain palliation with strontium-89 in cancer patients with bone metastases.

Strontium-89 is a pure beta-emitting radioisotope, a chemical analogue of calcium, and it is therefore avidly concentrated by areas of high osteoblastic activity. Selective uptake and prolonged retention at sites of increased bone mineral turnover provide precise bone lesions targeting. 89Sr chloride (commercialised as Metastron) is typically administered in a single 150 MBq parenteral dose. Its radioactive emission poses very little radioprotection concerns. Overall, studies show pain relief in up to 80% of patients, of which 10 to 40% became effectively pain free. The mean duration of palliation was 3-4 months. The mechanism of pain relief is controversial ; it is probably, but not only, related to the absorbed dose in the tumour and bone. There is no clear dose-response relationship. The only reported toxicity is temporary myelosuppression. WBC and platelets should be monitored at least on a weekly basis until they return to baseline. It seems that only patients with a reasonably good general condition stand to benefit from this treatment. In conclusion, systemic radionuclide therapy using 89Sr represents a feasible, safe, effective, well tolerated and cost-effective palliative treatment in patients with refractory bone pain.