Lutetium-177-PSMA-617 in Low Volume Metastatic Prostate Cancer

Radioligand therapy (RLT) is a promising new therapeutic approach to treat metastatic prostate cancer. This tumor-specific treatment is directed against prostate-specific membrane antigen (PSMA), which is overexpressed in prostate cancer cells. In the last few years, several lutetium-177 (177Lu, β emitter) labeled PSMA ligands have been developed and are currently applied in nuclear medicine departments world-wide to treat metastatic castrate resistant prostate cancer (mCRPC) patients. A large retrospective study reported an overall biochemical response rate of 45% following multiple 177Lu-PSMA RLT cycles in mCRPC patients, while 40% of patients already responded after a single cycle. RLT with PSMA ligand PSMA-617 was generally well tolerated and 12% of the patients suffered grade 3 to 4 hematological toxicity. In addition, mild and often transient xerostomia occurred in 8%. These results were confirmed in a smaller scale prospective study published recently. Although these results are very promising, it is noteworthy that all currently Lu-177-PSMA-617 RLT only has been evaluated in end stage prostate cancer patients to date. In theory, RLT could be more effective in low volume disease because of the very high tumor uptake of radioligands in small lesions. There are no published data so far evaluating the therapeutic effect of Lu-177-PSMA-617 RLT in an earlier stage of the disease. Because of the difference in tumor load between mCRPC patients and patients with low volume metastatic disease, dosimetry and toxicity in these patients need evaluation. Here a clinical trial to investigate the efficacy of Lu-177-PSMA-617 RLT in patients with low volume metastatic prostate cancer, prior to the hormone insensitive state is proposed. Objective: The aim of this study is to evaluate the dosimetry and toxicity of Lu-177-PSMA-617 RLT, in patients with low volume, hormone sensitive metastatic prostate cancer under treatment condition. Ultimately, the goal of this study is to stabilize previously progressive disease in these patients and to improve the quality of life by postponing the need for androgen deprivation therapy (ADT).