Strontium-89 (Metastron) in the treatment of prostate cancer metastatic to bone

Bone metastases that develop in patients with advanced prostate cancer often cause deep, unremitting pain. Palliative options for the control of this pain include analgesic support, cytotoxic chemotherapy and external-beam radiotherapy. In addition to external irradiation, interest in intravenously injected radioisotopes that are preferentially localized to bone has been mounting. Metastron (an isotope of strontium) imitates the biodistribution of calcium in vivo and is avidly taken up into bony metastases where it has a biological half-life of just over 50 days. The biological half-life in undiseased bone is far shorter, approximately 14 days. Various studies have been conducted to evaluate the role of Metastron in metastatic prostate cancer. An optimum dose has yet to be finalized, but it is clear that the change of haematological toxicity becomes more significant at much larger doses. In the large, randomized Trans Canada study in which Metastron or placebo was given to patients as an adjunct to local field irradiation, those patients treated with Metastron had a significantly reduced intake of analgesics. Furthermore, progression of pain, as measured either by sites of new pain or by the requirement for further palliative radiotherapy, demonstrated statistically significant differences in favour of Metastron. There is thus increasing evidence of a useful role for Metastron in the treatment of prostate cancer metastatic to bone.