PRIMARY OBJECTIVE:~I. To determine the 12-month radiographic progression-free survival rate per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 and Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria in patients with mCRPC treated with pembrolizumab and 177Lu-PSMA-617.~SECONDARY OBJECTIVES:~I. To determine the median radiographic progression-free survival per RECIST v. 1.1 and PCWG3 criteria in patients with mCRPC treated with pembrolizumab and 177Lu-PSMA-617.~II. To determine the objective response rate per RECIST v. 1.1 and PCWG3 criteria in patients with mCRPC treated with pembrolizumab and 177Lu-PSMA-617.~III. To determine the median duration of objective response per RECIST v. 1.1 and PCWG3 criteria in patients with mCRPC treated with pembrolizumab and 177Lu-PSMA-617.~IV. To determine the greater than 50% decline from baseline PSA (PSA50) and greater than 90% decline from baseline PSA (PSA90) response rate by PCWG3 criteria at any time point on study, as well as individually following each dose of 177Lu-PSMA-617.~V. To determine the median time to PSA progression (TTPP) following each dose of 177Lu-PSMA-617 (e.g., TTPP-1, TTPP-2, etc.), as measured by PCWG3 criteria.~VI. To determine the median overall survival in patients with mCRPC treated with pembrolizumab and 177Lu-PSMA-617.~VII. To characterize the safety profile of the combination of pembrolizumab and 177Lu-PSMA-617 in patients with mCRPC.~OUTLINE:~Participants will receive one dose of 177Lu-PSMA-617 and may continue treatment for up to six total doses, in the absence of unequivocal clinical progression, or unacceptable toxicity, with minimum interval of 6 weeks between doses. Participants will also receive pembrolizumab and may continue study treatment until unequivocal evidence of clinical progression or at physician's discretion based on clinical evaluation. Participants will undergo safety follow-up visits approximately 30 days following the end of treatment visit. After the last dose/discontinuation of study drug(s), participants will be seen in clinic or contacted by telephone every 3 months after their last treatment date to assess survival/disease/anti-cancer therapy status until death, withdrawal of consent, or the end of the study, whichever occurs first.
This is a single-center, open-label, study of Prostate-Specific Membrane Antigen (PSMA)-targeted radionuclide therapy with 177Lu-PSMA-617 in combination with pembrolizumab in participants with metastatic castrate-resistant prostate cancer (mCRPC) who have previously progressed on at least one prior androgen pathway inhibitor (e.g., abiraterone, enzalutamide, apalutamide).