After stopping treatment, 406 patients from the radium-223 group and 168 from the placebo group entered the trial’s posttreatment follow-up program. Nearly 60% had previously received docetaxel (Taxotere), and roughly 40% were receiving bisphosphonates, usually zoledronate (Zometa).
The majority of patients – 83% and 71%, respectively – had received all of the six planned injections of study drug, reported Dr. Nilsson.
There was a high rate of withdrawal of patients during the follow-up period, 79% in the radium-223 group and 86% in the placebo group, in the majority of cases due to death.
The median duration of follow-up was 10.4 months for the radium-223 group and 7.6 months for the placebo group.
Analyses of hematologic adverse events showed that the two groups had an identical rate of grade 3/4 anemia, at 1%.
The radium-223 group had a single case of grade 3/4 aplastic anemia, diagnosed by bone marrow biopsy and considered treatment related. "This was a patient who had received samarium and chemotherapy, and repeated external beam radiotherapy to his bone metastatic disease," Dr. Nilsson noted.
In addition, there were two cases each of grade 3/4 leukopenia and neutropenia in the radium-223 group, for an overall myelosuppression rate of about 3%.
Analyses of nonhematologic adverse events showed that the radium-223 group had single cases of grade 3-5 multiorgan failure, pneumonia, and pathologic fracture, while the placebo group had a single case of grade 3-5 cardiopulmonary failure.
None of the patients were reported to have developed acute myeloid leukemia, myelodysplastic syndrome, or primary bone cancer.
Primary cancers in other organs were seen in two patients in the radium-223 group (bladder cancer and lymph node metastases not originating from prostate cancer) and three in the placebo group (two cases of skin cancer and one of rectal cancer); all were considered unrelated to the study drug, according to Dr. Nilsson.
Dr. Nilsson disclosed that he is a consultant/adviser to Algeta and Bayer HealthCare. The trial was sponsored by Bayer in collaboration with Algeta. Dr. Morris disclosed that he is a consultant to Bayer.