ASCO: Radium-223 Helps in Hormone-Refractory Prostate Cancer

Radium-223, an investigational bone-seeking radioisotope, appeared to slow progression of skeletal metastases in hormone-refractory prostate cancer, researchers reported here. In a phase II study of 64 men, bone-alkaline phosphatase -- a marker for progression of hormone-refractory prostate cancer -- decreased by a median of 65.6% after four radium-223 treatments, said Øyvind S. Bruland, M.D., Ph.D., of the Norwegian Radium Hospital Trust in Oslo, Norway. This compared with a 9.3% increase in a placebo group (P<0.0001).
Dr. Bruland reported the findings during a poster discussion at the American Society of Clinical Oncology meeting and the results were published simultaneously online by The Lancet Oncology.
Dr. Bruland and colleagues enrolled 64 men at 11 centers in Sweden, Norway, and England from February 11, 2004 through May 3, 2005. Thirty-three men were randomized to external beam radiation plus four radium-223 injections and 31 to external beam radiation and saline injections.
Treatment lasted 12 weeks with injections at baseline and again at four-week intervals for a total of four injections.
From baseline to four weeks after the final radium-223 injection there was a median decrease of 23.8% in PSA versus a 44.9% increase in PSA in the placebo arm (P=0.003), they said.
Moreover, the median time to PSA progression was 26 weeks in the radium arm versus eight weeks for placebo (P=0.048, log rank).
Median overall survival was 65.3 weeks in the radium group versus 46.4 weeks in the placebo arm (P=0.066, log rank).
After 18 months of follow-up, 15 of the radium patients survived compared with eight assigned placebo, they wrote.
Dr. Bruland said the four injections of radium-223 were so well tolerated that his group is considering a study using a six-injection protocol.
Unlike other radioisotopes, radium-223 had little to no myelotoxic effect. He said this was not surprising since radium-223 was specifically chosen because it emits alpha radiation, which has higher energy and travels less distance than beta radiation.
"So it doesn't get into the bone marrow but has a significant effect on bone metastases," he said.
There was no significant difference in time to first skeletal-related event -- 14 weeks in the radium group and 11 weeks in the placebo group.
Dr. Bruland said, however, that the study has a number of limitations including its small sample size and the fact that all patients also received external-beam radiation.
Moreover, he noted that when the study was started docetaxel (Taxotere) was not really the standard of care in Scandinavia so radium-223 has not been evaluated in the setting of current standard treatment.