Phase II Randomised Controlled Trial of Patient-specific Adaptive vs. Continuous Abiraterone or eNZalutamide in mCRPC

Hormone tablets, abiraterone (Zytiga®) and enzalutamide (Xtandi®) are approved to treat advanced prostate cancer. However, even if these drugs are helpful, their effectiveness usually diminishes over time. Small pilot studies have indicated that using hormone tablets sparingly, for just long enough to control the cancer, followed by a break in treatment and restarting them later, seems to improve how long hormone tablets can control the cancer. This study aims to find out if this pause/restart strategy is better than taking hormone tablets every day continuously. The study will include 168 people with metastatic castrate resistant prostate cancer in the Netherlands and Australia. Patients will be randomly 1:1 assigned between the control group and the experimental group. In the control group, patients will take the treatment with AA/ENZ every day until the prostate cancer doesn't respond anymore to the treatment. In the experimental group, patients will start with daily AA/ENZ until the PSA has declined for \>50%. The treatment will then be paused and monthly PSA measurements will be performed. The treatment will be re-initiated when the PSA has increased to the level of before starting treatment. The treatment will be continued daily until the PSA has again dropped for \>50%. This pause/restart cycle will be repeated until the prostate cancer doesn't respond anymore to the treatment.