Targeting PSMA by radioligands in non-prostate disease-current status and future perspectives.

BACKGROUND: Prostate-specific membrane antigen (PSMA) is the up-and-coming target for molecular imaging of prostate cancer. Despite its name, non-prostate-related PSMA expression in physiologic tissue as well as in benign and malignant disease has been reported in various publications. Unlike in prostate cancer, PSMA expression is only rarely observed in non-prostate tumor cells. Instead, expression occurs in endothelial cells of tumor-associated neovasculature, although no endothelial expression is observed under physiologic conditions. The resulting potential for tumor staging in non-prostate malignant tumors has been demonstrated in first patient studies. This review summarizes the first clinical studies and deduces future perspectives in staging, molecular characterization, and PSMA-targeted radionuclide therapy based on histopathologic examinations of PSMA expression. CONCLUSIONS: The non-exclusivity of PSMA in prostate cancer opens a window to utilize the spectrum of available radioactive PSMA ligands for imaging and molecular characterization and maybe even therapy of non-prostate disease.

177Lu-PSMA-617 radioligand therapy and outcome in patients with metastasized castration-resistant prostate cancer.

PURPOSE: Radioligand therapies targeting prostate-specific membrane antigen (PSMA) have been established for the treatment of metastasized castration-resistant prostate cancer (mCRPC) in the last decade and show promising response rates and a favourable toxicity profile. The aim of this study was to evaluate the overall survival (OS) and to identify parameters predicting outcome in mCRPC patients treated with 177Lu-PSMA-617. METHODS: Between December 2014 and January 2017, 59 consecutive patients (median age 72 years; interquartile range, (IQR, 66-76 years) with mCRPC, who had been treated with at least one next-generation antihormonal drug as well as chemotherapy, were included in this study. Biochemical response was evaluated using Prostate Cancer Working Group 3 (PCWG3) criteria. Survival was evaluated using Kaplan-Meier estimates and Cox regression proportional hazards model. Toxicity was assessed using Common Toxicity Criteria for Adverse Events (CTCAE). The study was approved by the local ethics committee. RESULTS: The 59 patients were treated with a total of 159 cycles (median 3 cycles, range 1-7) of 177Lu-PSMA-617 (median dose 6.11 GBq, IQR 5.9-6.3 GBq). The median follow-up was 24 weeks (IQR 15-36 weeks). Follow-up data for at least 12 weeks (PCWG3) were available in 76% (45) of the patients. For outcome results data from all patients treated with at least one cycle were analysed. A decline in prostate-specific antigen (PSA) of ≥50% occurred in 53%, and a decline in PSA of any amount in 91% of patients. The estimated median OS was 32 weeks. An initial alkaline phosphatase (ALP) level <220 U/L and a PSA decline after the first cycle were associated with a longer OS (56 vs. 28 weeks, p < 0.01, and 56 vs. 29 weeks, p = 0.04, respectively). The median estimated PSA progression-free survival (PPFS) was 18 weeks. Only ALP level <220 U/L was significantly associated with a longer PPFS (41 vs. 18 weeks, p < 0.01). CONCLUSIONS: A PSA decline after the first cycle of 177Lu-PSMA-617 and an initial ALP level <220 U/L were predictors of a longer OS in patients with end-stage mCRPC. An ALP level <220 U/L was additionally associated with a longer PPFS.