A plain language summary of the EORTC 1333/PEACE-3 study of enzalutamide alone vs enzalutamide plus radium-223 in patients with metastatic castrationresistant prostate cancer (mCRPC) and bone metastases

What is this summary about? Enzalutamide and radium-223 are two different types of medicines normally used separately to treat prostate cancer that has spread to other parts of the body (metastatic castration-resistant prostate cancer; mCRPC). Both medicines are usually given with androgen deprivation therapy (ADT). Radium-223 is only used in people with mCRPC whose cancer has spread to their bones (called bone metastases). When the study began, enzalutamide was only used to treat patients with castration-resistant disease; nowadays, it is also used to treat earlier stages of prostate cancer that are hormone-sensitive. This summary describes the early results of a study called EORTC 1333, or 'PEACE-3'. The researchers compared enzalutamide plus ADT treatment alone against enzalutamide plus ADT combined with radium-223 in people with mCRPC with bone metastases who had not been treated for mCRPC. Patients, however, may have been treated for earlier stages of prostate cancer. They wanted to see if there was any difference in how long patients lived before their cancer got worse based on medical scans (radiological progression-free survival). They also looked for any difference in how long patients lived and the side effects of combining the two therapies. What were the results of the study? In people with mCRPC, combined treatment with enzalutamide plus ADT and radium-223 showed a trend towards an increased time that patients lived without their cancer getting worse compared with enzalutamide plus ADT alone. The combined treatment was also found to improve how long they lived. More people had broken bones (fractures) in the combination group, but the use of medication to keep bones strong partway through the study helped reduce the risk of fractures in both treatment groups. Most side effects were moderate and manageable. What do the results mean? In people not treated for mCRPC before, combining enzalutamide plus ADT with radium-223 treatment can slow down their cancer compared with taking enzalutamide plus ADT alone. The results suggest that people live longer if they have this combined treatment. Therefore, combining enzalutamide and radium-223 could be a new option for doctors to treat people with mCRPC with bone metastases. However, it should be given with medication to keep bones strong. It is worth noting that, when this study began, enzalutamide was mainly used to treat patients who had castration-resistant prostate cancer. Today, enzalutamide is used to treat earlier stages of prostate cancer. This means that treatments received for earlier stages of prostate cancer may differ between patients enrolled in PEACE-3 and those who are being treated in routine clinical practice today. Clinical trial number :.