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

Abiraterone and enzalutamide (AA/ENZ) are drugs which are being used to treat metastatic prostate cancer. These drugs are a form of additional hormonal therapy and have been used for many years. For most patients, these drugs work well and the prostate cancer stays under control for several months to years. In all patients, there will be a moment when the prostate cancer doesn't respond anymore to the treatment. This is called resistance. This leads to increasement of PSA, tumor growth on the CT-scan and/or bone scan or decline of condition. The investigators want to establish if it is possible to delay the development of resistance by using the drugs differently. It is now recommended to use AA/ENZ daily until the prostate cancer doesn't respond anymore to the treatment. During treatment, all cancer cells sensitive to treatment will die and all cells resistant for treatment will survive. Based on evolutionary principles, this might not be a wise strategy. The groups of resistant cancer cells will prevail and will grow faster and faster. This will lead to increasement of PSA, tumor growth on the CT-scan and/or bone scan or decline of condition. The investigators want to establish if it is better to not take the treatment drugs daily, but to pause the treatment on regular basis. The theory of the investigators is that, due to just in time pausing the treatment, a part of the treatment sensitive cells will remain alive. These treatment sensitive cancer cells will compete with the treatment resistant cells for limited space and nutrients. In this way, the treatment sensitive cancer cells prevent the accelerating growth of the treatment resistant cancer cells. Due to this phenomenon, the investigator hypothesis is the prostate cancer will respond longer to treatment. It will take longer until a new treatment is necessary or until a patients develops complaints. When the treatment is paused, patients might experience less side effects. It is easy to establish whether the prostate cancer responds to treatment by measuring PSA.