PSMA-RLT in Patients with Metastatic Hormone-Sensitive Prostate Cancer: A Retrospective Study

SIMPLE SUMMARY: Prostate-specific membrane antigen-direct radioligand therapy is a novel treatment for patients with castration-resistant prostate cancer. Yet, given the mode of action of PSMA-RLT, it is postulated that in early disease prostate cancer settings, e.g. hormone-sensitive, can also benefit from this treatment. In this retrospective study, the safety and efficacy was investigated of two PSMA-RLT schemes: monotherapy with 177Lu-PSMA and 177Lu-PSMA in combination with 225Ac-PSMA in twenty patients with early stage metastatic prostate cancer. The treatment appeared safe with limited and mainly transient side effects, also on a longer term follow-up, with encouraging efficacy for twenty early-stage metastatic prostate cancer. ABSTRACT: Background: Prostate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) is a novel treatment for patients with castration-resistant prostate cancer (CRPC). Given the mode of action, patients in an earlier disease stage, such as hormone-sensitive prostate cancer (HSPC), are also likely to benefit from [(177)Lu]Lu-PSMA- ((177)Lu-PSMA) or [(225)Ac]Ac-PSMA-radioligand treatment ((225)Ac-PSMA). In this retrospective study, we analyzed the safety and efficacy of PSMA-RLT in early-stage and hormone-sensitive metastatic prostate cancer patients. Methods: A retrospective study was performed in patients who received (177)Lu-PSMA and/or (225)Ac-PSMA with early-stage metastatic prostate cancer. The primary outcome parameter evaluated in this study was the progression-free survival (PFS) after PSMA-RLT and toxicity according to the Common Terminology Criteria for Adverse Events. Secondary outcome parameters were prostate-specific antigen (PSA) response and the date of onset of CRPC state. Results: In total, 20 patients were included of which 18 patients received (177)Lu-PSMA radioligand and two patients received tandem treatment with both (177)Lu-PSMA and (225)Ac-PSMA radioligands. Patients received a median of 2 treatment cycles (range 1–6) and a median activity of 6.2 GBq (177)Lu-PSMA per cycle (interquartile range (IQR) 5.2–7.4 GBq). PSMA-RLT was overall well-tolerated. The most common grade 1–2 side effects were xerostomia (n = 6) and fatigue (n = 8), which were only temporarily reported. One patient that received (225)Ac-PSMA developed grade 3–4 bone marrow toxicity. The median PFS was 12 months (95% confidence interval (CI), 4.09–19.9 months). Seventeen (85%) patients had a ≥50% PSA response following PSMA-RLT. One patient developed CRPC 9 months following PSMA-RLT. Conclusions: In this small cohort study, PSMA-RLT appeared safe and showed encouraging efficacy for (metastasized) early-stage and hormone-sensitive prostate cancer patients. Prospective studies are awaited and should include long-term follow-up.