Lutetium-177-PSMA-I&T

In recent years, there is increasing evidence showing a beneficial outcome (e.g. progression free survival; PFS) after metastases-directed therapy (MDT) with external beam radiotherapy (EBRT) or targeted surgery for oligometastatic hormone sensitive prostate cancer (oHSPC). However, many patients do not qualify for these treatments due to prior interventions or tumor location. Such oligometastatic patients could benefit from radioligand therapy (RLT) with 177Lu-PSMA; a novel tumor targeting therapy for end-stage metastatic castration-resistant prostate cancer (mCRPC). Especially because RLT could be more effective in low volume disease, such as the oligometastatic status, due to high uptake of radioligands in smaller lesions. To test the hypothesis that 177Lu-PSMA is an effective treatment in oHSPC to prolong PFS and postpone the need for androgen deprivation therapy (ADT), we initiated a multicenter randomized clinical trial. This is globally, the first prospective study using 177Lu-PSMA-I&T in a randomized multicenter setting.

This study compares 177Lu-PSMA-I&T MDT to the current standard of care (SOC); deferred ADT. Fifty-eight patients with oHSPC (≤5 metastases on PSMA PET) and high PSMA uptake (SUVmax > 15, partial volume corrected) on 18F-PSMA PET after prior surgery and/or EBRT and a PSA doubling time of < 6 months, will be randomized in a 1:1 ratio. The patients randomized to the interventional arm will be eligible for two cycles of 7.4GBq 177Lu-PSMA-I&T at a 6-week interval. After both cycles, patients are monitored every 3 weeks (including adverse events, QoL- and xerostomia questionnaires and laboratory testing) at the outpatient clinic. Twenty-four weeks after cycle two an end of study evaluation is planned together with another 18F-PSMA PET and (whole body) MRI. Patients in the SOC arm are eligible to receive 177Lu-PSMA-I&T after meeting the primary study objective, which is the fraction of patients who show disease progression during the study follow up. A second primary objective is the time to disease progression. Disease progression is defined as a 100% increase in PSA from baseline or clinical progression.

This is the first prospective randomized clinical study assessing the therapeutic efficacy and toxicity of 177Lu-PSMA-I&T for patients with oHSPC.

Clinicaltrials.gov identifier: NCT04443062.

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is increasingly being used in metastatic castration-resistant prostate cancer (mCRPC). The objective of this study is to report our clinical experience with RLT using 177-lutetium-labeled PSMA-I&T. A total of 100 patients were treated under a compassionate use protocol with a total number of 319 cycles (median two cycles, range 1-6). Eligibility criteria included previous treatment with abiraterone or enzalutamide, previous taxane-based chemotherapy or chemoineligibility, and positive PSMA-ligand uptake at positron-emission tomography scan. The ¹⁷⁷Lu-PSMA-I&T was given 6-8 weekly with an activity of 7.4 GBq up to six cycles. The median number of previous mCRPC regimens was 3 (range 1-6), and 35 patients had visceral metastases. Prostate-specific antigen decline of ≥50% was achieved in 38 patients, median clinical progression-free survival (cPFS) was 4.1mo, and median overall survival (OS) was 12.9mo. Subgroup analyses identified an association of visceral metastases with a poor prostate-specific antigen (PSA) response and shorter cPFS and OS, and an association of rising lactate dehydrogenase (LDH) with shorter cPFS and OS. Patients achieving PSA decline of ≥50% within 12wk of treatment showed longer cPFS and OS. Treatment-emergent hematologic grade 3/4 toxicities were anemia (9%), thrombocytopenia (4%), and neutropenia (6%). Grade 3/4 nonhematologic toxicities were not observed. RLT with ¹⁷⁷Lu-PSMA-I&T showed good activity in more than one-third of patients with late-stage mCRPC at low toxicity. Presence of visceral metastases and rising LDH were associated with worse treatment outcome. PATIENT SUMMARY: We analyzed the treatment outcome and toxicity of prostate-specific membrane antigen-targeted radioligand therapy in patients with metastatic castration-resistant prostate cancer. We found that a good treatment response could be achieved in a subgroup of patients with few side effects. We also observed that treatment outcome was worse in patients with organ metastases and elevated lactate dehydrogenase in blood tests.