Prostate-specific membrane antigen (PSMA) radioligand therapy (RLT) is a promising new therapeutic approach to treat metastatic prostate cancer. This tumor-specific treatment is directed against PSMA, which is overexpressed in prostate cancer cells. In the last few years, several Lutetium-177 (177Lu, emitter) labeled PSMA ligands have been developed and are currently applied in nuclear medicine departments worldwide 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 177Lu-PSMA 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%. A prospective study carried out in Australia confirmed these results recently. Based on these outcomes Endocyte (a Novartis company) is currently carrying out an international multicenter prospective registration study for end-stage mCRPC patients (NCT03511664).

Although these results are promising, it is noteworthy that most of the currently available data is retrospective and 177Lu-PSMA has only been evaluated in end stage prostate cancer patients to date. However, based on the mode of action, 177Lu-PSMA could also be effective in low volume disease because of the very high tumor uptake of radioligands in smaller lesions. Also, in a pilot study (NCT03828838) we were able to show that 177Lu-PSMA treatment is safe coupled with promising response rates. Hence, the present randomized trial to investigate the efficacy of 177Lu-PSMA in patients with oligo-metastatic (5 metastases) metastatic prostate cancer, prior to the hormone insensitive state. In this study, 58 patients will be included in a 1:1 ratio to receive either 177Lu-PSMA or the current standard of care (deferred androgen deprivation therapy).

At the end of the study period for answering the primary research question, patients randomized to the control arm are eligible to receive 177Lu-PSMA if they meet the end of the study period treatment (EOT 1) criteria and are willing to undergo 177Lu-PSMA.

EOT 1 is defined by:

• Clinical progression determined by the treating physician (e.g. increasing pain from metastases)
• A 100% increase in PSA after cycle one blood draw (BASELINE) during study. Exception: PSA increase in the first 12 weeks after the first treatment injection as was defined by the PCWG3 criteria.