Delayed response after repeated 177Lu-PSMA-617 radioligand therapy in patients with metastatic castration resistant prostate cancer

Purpose Radioligand therapy (RLT) using Lutetium-177 labeled PSMA-617 (Lu-PSMA) ligand is a new therapeutic option for salvage therapy in heavily pretreated patients with metastatic castration resistant prostate cancer. The aim of this retrospective study was to analyze response in patients receiving 3 cycles of Lu-PSMA. Methods Seventy-one patients (median age: 72 years; range 44-87) received 3 cycles of RLT with Lu-PSMA (mean administered activity: 6.016 +/- 0.543 GBq) every 8 weeks. Response was evaluated using serum PSA levels and a PSA decline >= 50% was considered as biochemical response. Additionally, any PSA decline after the first cycle was evaluated for further therapy effects after the second and third cycle. Results A total of 213 cycles were performed in 71 patients. Data for response and adverse events were available for all patients. A PSA decline >= 50% and some PSA decline occurred in 56% and 66% of the patients. Of 30 patients with a PSA response after the first cycle, 28 remained responders and 12/41 of non-responders responded to further therapy cycles. Conclusion RLT with Lu-177-PSMA-617 shows respectable response rates. In this retrospective analysis, a relevant number of patients showed a delayed response, even if they did not respond to the first cycle of the therapy.