5549 Background: This was an open-label randomized prospective bi-centric single-arm phase II clinical trial of 177Lu-PSMA-617 molecular radiotherapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC) conducted at University of California Los Angeles (USA) and Excel Diagnostics & Nuclear Oncology Center (Houston, TX, USA) (NCT03042312). The study was investigator-initiated under an investigational new drug approval protocol (IND#133661) with authorization of charging for investigational drug (cost-recovery, Title 21 CFR 312.8). We report here the post-hoc analysis of overall survival (OS) in a single-study site cohort (UCLA). Methods: Patients with progressive mCRPC (biochemical, radiographic, or clinical) after ≥1 novel androgen axis drug (NAAD), either chemotherapy (CTX) naïve or post-CTX, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA-target expression by PET were eligible. Patients received up to 4 cycles of 177Lu-PSMA-617 every 8±1 weeks and were randomized into 2 treatment activities groups (6.0 or 7.4 GBq). Efficacy was defined as serum PSA decline of ≥50% from baseline and served as primary endpoint (hypothesis: ≥40% of responders after 2 cycles). Results: 43 patients were randomized to the 6.0 GBq (n= 14) and 7.4 GBq (n=29) treatment arms. 11/43 (26%) were CTX naïve while 10/43 (23%), 12/43 (28%), 5/43 (12%) and 5/43 (12%) had received 1, 2, 3 or 4 CTX regimens. Median baseline PSA was 29.2 ng/ml (mean 228.8, range 0.5-2082.6). 21/43 (49%) completed 4 cycles of 177Lu-PSMA-617 whereas 4/43 (9%), 13/43 (30%) and 5/43 (12%) underwent 1, 2 and 3 cycles. PSA decline of ≥50% was observed in 11/43 of patients (26%) after 2 cycles and in 16/43 (37%) at any time (best PSA response). 9/43 (21%) had a PSA decline of ≥90% and 23/43 (53%) had any PSA decline (>0%). After a median follow-up of 19.5 months the median OS was 14.8, 15.7 and 13.5 months in the whole cohort, the 6.0 GBq and 7.4 GBq treatment arms, respectively (p=0.68). Patients showing a PSA decline of ≥50% after 2 cycles and at any time had a longer OS: median 20.1 months vs. 13.6 (p=0.091) and 20.1 vs. 11.6 (p=0.002), respectively. Conclusions: In this post-hoc analysis of a single-site cohort of 43 patients included in a prospective phase II trial the median OS after 177Lu-PSMA-617 molecular radiotherapy in patients with progressive mCRPC was 14.8 months. There was no difference of efficacy between the 6.0 GBq and 7.4 GBq treatment arms. Clinical trial information: NCT03042312 .
Applying radiobiology to clinical molecular radiotherapy
