Efficacy and safety of rechallenge [177Lu]Lu-PSMA-617 RLT after initial partial remission in patients with mCRPC: evaluation of a prospective registry (REALITY study).

Aim: Rechallenge of [¹⁷⁷Lu]Lu-PSMA-617 radioligand therapy (RLT) was proposed for patients who initially responded to PSMA-RLT experiencing partial remission, but relapsed into progression after a certain period of remission. However, only limited data is available regarding this approach. In this study, we analyzed the efficacy and safety profile of one or more series of [¹⁷⁷Lu]Lu-PSMA-617 RLT rechallenge in patients from a prospective registry (REALITY Study, NCT04833517) after they initially benefited from PSMA-RLT.

Methods: Forty-seven patients with metastatic castration-resistant prostate cancer (mCRPC) who had biochemical response to initial [¹⁷⁷Lu]Lu-PSMA-617 RLT followed by disease progression received at least one (up to three) series of [¹⁷⁷Lu]Lu-PSMA-617 RLT rechallenge. Biochemical response rates based on prostate-specific antigen (PSA) serum value, PSA-based progression-free survival (PFS) and overall survival (OS) were calculated. Adverse events of the treatment were assessed according to 'common terminology criteria for adverse events' (CTCAE).

Results: After one series of RLT rechallenge, a PSA decline of at least 50% was achieved in 27/47 patients (57.4%). The median PFS of all patients was 8.7 mo and the median OS was 22.7 mo, each calculated from the administration of the first rechallenge series. Patients who responded (PSA decline > 50%) to the rechallenge showed a median OS of 27.3 mo. Regarding PFS, a significant correlation (r = 0.4128, p = 0.0323) was found for these patients comparing initial and rechallenge RLT. Ten patients received a second and 3 patients received a third rechallenge series with 8/10 and 3/3 patients responding to repeated RLT rechallenge. No severe deterioration of adverse events rated by CTCAE criteria was observed.

Conclusion: [¹⁷⁷Lu]Lu-PSMA-617 RLT rechallenge is associated with significant PSA response and encouraging survival outcome as well as a very favourable safety profile and should therefore be considered as a straight-forward treatment option in mCRPC patients, who previously benefited from PSMA-RLT.