Leukapheresis

The goal of this observational study is to compare the number of CTCs enriched by both sampling methods, leukapheresis and collection of peripheral blood in metastatic prostate cancer patients. The main questions it aims to answer are: 1. The advantages and disadvantages of two sampling methods for further diagnosis and treatment; 2. How to obtain further information on the tumour biology of CTC; 3. The mechanisms of prostate cancer invasion and metastasis Participants will have 7.5mL of peripheral blood taken as well as undergo leukapheresis.