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.

Inclusion Criteria:

1. male, aged 18-75 years; and
2. Evidence of metastasis (positive finding of metastasis on one of the following tests: CT and MRI; whole-body nuclear bone imaging, fluoride PET and PET-CT, cholinergic PET-CT and MRI; prostate-specific membrane antigen-targeted PET-CT); or clinical diagnosis of metastatic prostate cancer (tumour stage of T3 and above) by pathology of aspiration/surgical biopsy;
3. Good general condition, ECOG score 0-1, able to tolerate leukapheresis;
4. Normal haematological analysis, liver and renal function tests at screening;
5. Subjects (or their legal representatives) can understand the informed consent form.

Exclusion Criteria:

1. those who have received systemic combination therapy for tumours within 5 years;
2. those with poor general condition, severe haemodynamic instability, malignant arrhythmias, cachexia and infections
3. those with coagulation disorders, DIC or reduced platelets;
4. those receiving exogenous plasma at the time of the trial;

Patients with metastatic prostate cancer with the following specific subject recruitment criteria:

1. Clinical diagnosis of metastatic prostate cancer with tumour stage of T3 or above;
2. Metastatic signs on relevant imaging tests, including CT and MRI, whole-body nuclear bone imaging, fluoride PET and PET-CT, cholinergic PET-CT and MRI, and prostate specific membrane antigen (PSMA)-targeted PET-CT;
3. After radical prostatectomy for prostate cancer with indication of biochemical recurrence (PSA>0.2ng/mL);
4. Those with metastatic prostate cancer diagnosed by puncture or postoperative pathology;
5. Previous medical history and treatment history.