Utilising CTC Counts to Optimize Systemic Therapy of Metastatic Prostate Cancer

Patients with metastatic castration-resistant prostate cancer will be randomised 1:1 to either control group (standard of care) or intervention group (CTC-guided treatment). All patients will commence first line chemotherapy with docetaxel three-weekly and will receive a minimum of 3 cycles of treatment before any recommendation to discontinue first-line docetaxel. * Control Group (standard of care): patients will receive first line docetaxel until disease progression according to treating clinician or completion of 10 cycles. Patients and treating clinicians will not be disclosed to the results of CTC determinations. * Intervention Group (CTC guided treatment): patients will receive first line docetaxel until progression by CTC, and/or disease progression according to treating clinician or completion of 10 cycles. CTC results will be available to the treating clinician to guide decision-making. A progressing CTC count on Day 1 will require confirmation with a second CTC count performed on Day 15 (-/+ 5 days) of that cycle. If a patient is found to have two successive CTC determinations showing progression by CTCs, the clinician will receive a recommendation to discontinue docetaxel on the following cycle. The reasons of the treating clinician to discontinue docetaxel will be reported in both groups. Patients who discontinue first line docetaxel according to the criteria for each group will be switched to second line chemotherapy with cabazitaxel. After progression on cabazitaxel or completion of 10 cycles, patients will be followed up for survival every three months until end of study.