RecruitingPhase 1Drug trialPilot Study for Detection of PSMA-Low CRPC-NE Tumors With Fluciclovine PET/CTThis research study is studying a positron emission tomography (PET) agent called 18F-fluciclovine to evaluate how well 18F-fluciclovine-PET scans determine the extent of advanced prostate cancer that either has low prostate-specific membrane antigen (PSMA) expression or has neuroendocrine features. The name of the study interventions are: * 18F-fluciclovine-PET/CT scan * Two research blood collections