A Pragmatic Randomised, Multicentre Trial Comparing 4-weekly Versus 12-weekly Administration of Bone-targeted Agents in Patients With Bone Metastases From Either Castration-resistant Prostate Cancer or Breast Cancer - The REaCT-BTA Study

Bone metastases are common in patients with advanced breast and prostate cancers. Skeletal metastases can be associated with reduced Quality of Life (QoL), pain and skeletal-related events (SREs) (defined as pathological fractures, surgery/radiotherapy to bone, spinal cord compression and hypercalcaemia). Maintaining QoL while avoiding or delaying SREs are the main goals of therapy. Patients therefore receive bone-targeted agents (e.g. pamidronate, zoledronate and denosumab) which are typically given every 4 weeks. However, this 4 week dosing is based on convenience so the treatment could be given concurrently with chemotherapy. The half-life of these drugs in the bone is many months or even years. Hence studies have been performed evaluating 12-weekly therapy. These have confirmed similar palliative outcomes in the 4 vs 12-weekly groups for both breast and prostate cancer patients. However, there remains clinical equipoise about which dosing interval physicians prescribe. The current trial will compare these two schedules of bone-targeting agents (12- vs. 4-weekly) to evaluate quality of life, pain and skeletal events within the Canadian Health Care System. This study will use an "integrated consent model" that involves "oral consent" rather than a written informed consent writing process as the study is comparing standard schedules and not a new administration schedule.