In this study, the investigators intend to validate 18F-DCFPyL test-retest reproducibility in metastatic lesions, in order to investigate whether it serves as a reliable response assessment tool, both to interpret existing studies and to design future longitudinal trials.

The investigators will image patients with widely metastatic castration-sensitive (CSPC) or castration-resistant prostate cancer (CRPC) using 18F-DCFPyL-PET/CT for detection of tumor burden and perform a lesion-based head-to-head comparison with a subsequent near-term (one to seven days) 18F-DCFPyL-PET/CT follow-up scan, to assess test-retest reproducibility of this second-generation PSMA-targeted compound. Second, as it has not been specifically investigated with this compound before, intra-observer agreement as well as inter-scan variability will be assessed.

Inclusion Criteria:

• Willing and able to provide written informed consent
• History of histologically or cytologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell histology
• Patients with metastatic castration-sensitive (CSPC) or castration-resistant prostate cancer (CRPC) with evidence of metastatic disease on conventional imaging with CT or bone scan.
• Prior docetaxel-based chemotherapy is permitted
• Documented metastatic prostate cancer progression as assessed by the treating oncologist with either one or both of the following and has not initiated a new therapy after determination of progression: Rising PSA over a minimum 1-week interval and/or radiographic progression in soft tissue and bone metastases (combination of bony and soft tissue metastases)
• Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2

Exclusion Criteria:

• Serious or uncontrolled co-existent non-malignant disease, including active and uncontrolled infection
• Administered a radioisotope ≤5 physical half-lives prior to the date of study PET/CT
• Administered IV X-ray contrast medium ≤24 hours prior to the date of study PET/CT
• Administered oral contrast medium ≤120 hours prior to the date of study PET/CT
• Condition or situation which, in the investigator's opinion, may put the patient at significant risk, may confound the study results, or may interfere significantly with patient's participation in the study