Treatment Outcome, Toxicity, and Predictive Factors for Radioligand Therapy with ¹⁷⁷Lu-PSMA-I&T in Metastatic Castration-resistant Prostate Cancer

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.