68Ga-PSMA-11 PET for the Diagnosis of Metastatic Castration Resistant Prostate Cancer

PRIMARY OBJECTIVE: I. To determine whether the percent change from baseline to 16 weeks (+/- 8 weeks) in maximum standard uptake value (SUVmax) averaged across up to 16 lesions per patient (SUVmax-ave) is associated with \>= 50% decline from baseline in serum prostate specific antigen (PSA50) response. SECONDARY OBJECTIVES: I. To determine whether the percent change from baseline in SUVmax-ave on PSMA PET is associated with time-to-event endpoints including PSA progression-free survival and overall survival. II. To determine whether the percent change from baseline in SUVmax on PSMA PET is associated with objective response by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 on a per-lesion basis among measurable soft tissue lesions present at baseline. EXPLORATORY (CORRELATIVE) OBJECTIVES: I. To descriptively characterize the histologic, transcriptional, and genomic features of PSMA low/negative lesions among patients who undergo paired optional metastatic tumor biopsy. II. To descriptively characterize the relationship between SUVmax-ave on baseline Ga-PSMA PET with optional baseline fludeoxyglucose F-18 (FDG)-PET. III. To determine whether heterogeneity of PSMA expression on baseline Ga-PSMA PET is associated with overall survival. IV. To descriptively characterize the patterns of PSMA expression at the time of disease progression among patients who undergo optional PSMA PET. V. To determine whether the percent change from baseline in PSMA PET is associated with PSA50 response among subgroups of patients defined by treatment modality received, including androgen receptor (AR) targeting treatment, PSMA-targeting radioligand therapy, cytotoxic chemotherapy, and immunotherapy. OUTLINE: Patients receive gallium Ga 68-PSMA-11 intravenously (IV) and undergo PET at baseline, 16 weeks after initiating therapy, and at time of disease progression. After progression or study completion, patients are followed up every 3 months for up to 24 months