Final overall survival and safety analyses of the phase III PSMAfore trial of [177Lu]Lu-PSMA-617 versus change of androgen receptor pathway inhibitor in taxane-naive patients with metastatic castration-resistant prostate cancer

Abstract

Background: In PSMAfore, [¹⁷⁷Lu]Lu-PSMA-617 (¹⁷⁷Lu-PSMA-617) prolonged radiographic progression-free survival (rPFS) in taxane-naive patients with metastatic castration-resistant prostate cancer (mCRPC), with a favourable safety profile, versus a change in androgen receptor pathway inhibitor (ARPI). We report the final overall survival (OS) analysis and updated safety data.

Patients and methods: PSMAfore (NCT04689828) was an open-label, international, phase III trial. Patients with prostate-specific membrane antigen (PSMA)-positive mCRPC who had experienced disease progression once on a previous ARPI and were candidates for ARPI change were randomized 1 : 1 to ¹⁷⁷Lu-PSMA-617 or ARPI change to abiraterone or enzalutamide. Crossover from ARPI change to ¹⁷⁷Lu-PSMA-617 was allowed after centrally confirmed radiographic progression. Endpoints included rPFS (primary), OS (key secondary), and safety (secondary).

Results: Patients were randomized to ¹⁷⁷Lu-PSMA-617 or ARPI change (n = 234 each): 141/234 participants (60.3%) randomized to ARPI change crossed over (75.4% of those with centrally confirmed radiographic progression). The median OS was 24.48 months [95% confidence interval (CI) 19.55-28.94 months] with ¹⁷⁷Lu-PSMA-617 versus 23.13 months (95% CI 19.61-25.53 months) with ARPI change [hazard ratio (HR) 0.91, 95% CI 0.72-1.14, P = 0.20] based on the intention-to-treat (ITT) principle; the crossover-adjusted OS HR by inverse probability of censoring weighting modelling was 0.59 (95% CI 0.38-0.91). For ¹⁷⁷Lu-PSMA-617 versus ARPI change, exposure-adjusted incidences of grade ≥3 and serious treatment-emergent adverse events were 60.8 versus 85.1 and 32.5 versus 49.9 per 100 patient-treatment years, respectively. Dry mouth occurred in 135/227 participants (59.5%; 2/227 grade ≥3) and anaemia in 62/227 (27.3%; 14/227 grade ≥3) in the ¹⁷⁷Lu-PSMA-617 arm.

Conclusions: OS analyses did not show a statistically significant difference between the ¹⁷⁷Lu-PSMA-617 and ARPI arms based on the ITT principle; results were likely confounded by the high rate of crossover. The safety profile of ¹⁷⁷Lu-PSMA-617 was favourable with no new safety signals identified.

Keywords: (177)Lu-PSMA-617; metastatic castration-resistant prostate cancer; overall survival; radioligand therapy; safety; taxane-naive.

Figure 1.. Intention-to-treat analysis of overall survival (key secondary efficacy endpoint).

ARPI, androgen receptor pathway inhibitor; CI, confidence interval; no., number; PSMA, prostate-specific membrane antigen.

Figure 2.. Incidence of haematologic TEAEs by number of ¹⁷⁷Lu-PSMA-617 administrations and number of bone metastases at baseline.

(A) Proportion of participants with haematologic TEAEs occurring at 1–4 versus 5–6 administrations of ¹⁷⁷Lu-PSMA-617, among participants who received 5 or 6 administrations ¹⁷⁷Lu-PSMA-617 (n = 165). (B) Proportion of participants with haematologic TEAEs according to number of bone metastases at baseline (0^a: ¹⁷⁷Lu-PSMA-617 n = 29, ARPI change n = 30; 1–5: ¹⁷⁷Lu-PSMA-617 n = 80, ARPI change n = 84; 6–20: ¹⁷⁷Lu-PSMA-617 n = 69, ARPI change n = 84; or >20/superscan: ¹⁷⁷Lu-PSMA-617 n = 49, ARPI change n = 34). Adverse events were coded using Common Terminology Criteria for Adverse Events v5.0 grading and Medical Dictionary for Regulatory Events v27.1 terms. ^aParticipants with a nonevaluable number of lesions are counted in the ‘0 bone metastases at baseline’ subgroup. ^bIncludes haemoglobin decreased. ^cIncludes lymphocyte count decreased. ^dIncludes neutrophil count decreased (panel A and B) and febrile neutropenia (panel B only). ^eIncludes platelet count decreased. ^fIncludes white blood cell count decreased. ARPI, androgen receptor pathway inhibitor; No., number; PSMA, prostate-specific membrane antigen; TEAEs, treatment-emergent adverse events.