A new radiotherapy drug for patients with prostate cancer that has spread to the bone

This phase 3 clinical trial assessed the efficacy and safety of radium-223 dichloride or radium-223 (Xofigo) in patients with prostate cancer that has spread to the bone. 

Testosterone, the main male sex hormone, promotes the growth of prostate cancer. A treatment option for prostate cancer patients is castration therapy. This treatment aims at lowering testosterone levels either by drugs that stop testosterone from getting to the prostate cancer (hormonal therapy) or by surgical removal of the testicles (the main organ that makes testosterone). This causes the prostate cancer to stop growing or even shrink. However, in many patients the cancer becomes resistant to castration therapy and keeps growing in spite of the lack of testosterone. This is referred to as castration-resistant prostate cancer (CRPC). Eventually the cancer may spread to other organs and tissues in the body (metastatic CRPC).

Bones are often the first site of prostate cancer metastasis. Bone metastases lead to a rapid removal of old bone and replacement with new one (increased turnover or bone metabolism), which can lead to bone destruction. This can cause skeletal symptoms such as bone pain, fractures, compression of the spinal cord or high calcium levels (by releasing calcium, the main mineral in the bone, into the blood stream). Radium-223 is a newly FDA approved (May 15th 2013) radiotherapy drug that is injected into a vein, for the treatment of patients with CRPC and bone metastases. Radium-223 is similar to calcium and binds to areas of increased bone turnover in bone metastases. It uses a type of radiation called alpha particles that kill cancer cells only in the bone, thus limiting the damage to other cells in the body. 

921 patients with CRPC and bone metastases were included in this study. 614 patients were randomly assigned to receive 6 injections (1 injection in 4 weeks) of radium-223 and 307 received a placebo (a substance with no medical effect used when testing new drugs). Additionally, all patients received the best treatments possible for their cancer. The main parameters evaluated were overall survival (the time patients survived after treatment) and time until patients experienced a skeletal symptom because of bone metastases. 

Results showed that overall survival was 30% higher in patients in the radium-223 group compared to placebo (14.9 months versus 11.3 months). Treatment with radium-223 significantly prolonged time until a skeletal event compared to placebo (15.6 months versus 9.8 months). The most common side effect reported was a higher risk of developing an infection. However, patients treated with radium-223 experienced fewer side effects than patients treated with placebo. 

In summary, radium-223 dichloride was safe and significantly improved overall survival and skeletal symptoms in patients with castration-resistant prostate cancer and bone metastases.

This clinical trial served as grounds for the FDA approval of Xofigo for patients with CRPC that has spread to the bones. This study was funded by Bayer HealthCare Pharmaceuticals and Algeta, the manufacturers of Xofigo.

Ask your doctor whether radium-223 is a good treatment option in your situation.