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.