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16 Background: In PSMAfore (NCT04689828), [ 177 Lu]Lu-PSMA-617 ( 177 Lu-PSMA-617) prolonged rPFS versus androgen receptor pathway inhibitor (ARPI) change in taxane-naive adults with PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) progressing once on an ARPI. Baseline circulating tumor DNA (ctDNA) fraction was associated with rPFS at the second interim analysis (IA) of OS (ASCO 24). Here, we assessed the association of baseline and cycle 2 day 1 (C2D1) ctDNA fraction, and early ctDNA and prostate-specific antigen (PSA) dynamics, with rPFS and OS at the third IA of OS. Methods: Patients were randomized 1:1 to 177 Lu-PSMA-617 (7.4 GBq Q6W; x6) or ARPI change. Endpoints included rPFS (primary) and OS (key secondary). Plasma ctDNA fraction was analyzed at baseline and at C2D1 using an in-house custom panel. Cox regression (adjusted for 3 risk classes based on clustering of 17 baseline clinical features) and random forest (adjusted for 15 baseline clinical features) modeling were used to assess the association of ctDNA fraction and PSA with clinical outcomes at the Feb-27-2024 data cutoff. Results: Patients with plasma samples at baseline and C2D1 were included ( 177 Lu-PSMA-617, n/N = 82/234; ARPI change, n/N = 91/234). Cox regression models adjusted for clinical features in the 177 Lu-PSMA-617 arm showed that higher ctDNA fraction was associated with shorter rPFS and OS (Table). These associations were stronger for C2D1 than baseline, both when comparing individual models and within a model including both timepoints (Table). In random forest models including clinical features and C2D1 ctDNA fraction, the total area under curves were not improved by addition of baseline ctDNA fraction (rPFS, 0.87; OS, 0.86). In the overall population, fractional decreases from baseline to C2D1 in ctDNA ( p = 0.0015) and PSA ( p < 0.0001) were strongly associated with longer rPFS, and were weakly correlated with one another (correlation coefficient, 0.26). In the 177 Lu-PSMA-617 arm, fractional decrease in ctDNA ( p = 0.002) was more strongly correlated with OS than was decrease in PSA ( p = 0.12). Conclusions: This exploratory analysis suggested that C2D1 ctDNA fraction was more strongly associated than baseline ctDNA fraction with rPFS and OS. Early ctDNA fraction dynamics contributed additional information in the prediction of rPFS and OS beyond PSA dynamics alone. Clinical trial information: NCT04689828 . Cox regression models. a rPFS OS Baseline model, HR (95% CI); p 6.0 (1.6–23.0); 0.0095 12.0 (3.0–48.7); 0.00052 C-index ± SE 0.69 ± 0.04 0.75 ± 0.04 C2D1 model, HR (95% CI); p 47.7 (10.1–226.0); < 0.0001 82.7 (16.4–417.0); < 0.0001 C-index ± SE 0.72 ± 0.03 0.77 ± 0.03 Baseline + C2D1 model Baseline, HR (95% CI); p 3.1 (0.7–14.0); 0.14 2.1 (0.4–12.7); 0.41 C2D1, HR (95% CI); p 35.9 (7.2–180.0); < 0.0001 52.5 (7.6–362.0); < 0.0001 C-index ± SE 0.72 ± 0.03 0.79 ± 0.03 a HRs correspond to 1 unit change in ctDNA fraction.

155 Background: Primary results from the randomized, multicenter, open-label, phase 3 TRITON3 (NCT02975934) study of rucaparib, a poly(ADP-ribose) polymerase inhibitor (PARPi) in patients with chemotherapy-naive mCRPC and BRCA1/2 (BRCA) vs the control arm of physician’s choice of DTX or ARPI (abiraterone acetate [ABI] or enzalutamide [ENZ]) demonstrated that rucaparib significantly improved radiographic progression-free survival (rPFS, primary efficacy endpoint) vs physician’s choice. Here, we report final OS and safety results from TRITON3. Methods: Patients with disease progression after 1 prior second-generation ARPI in any setting were randomized 2:1 to rucaparib 600 mg BID or physician’s choice of DTX, ABI, or ENZ (control). OS was a key secondary endpoint tested initially in the BRCA subgroup, followed by the intent-to-treat (ITT) population in an ordered step-down multiple-comparisons procedure. Crossover from placebo to rucaparib was allowed after radiographic progression was confirmed by independent radiology review. Results: As of March 1, 2024 (final analysis data cutoff),patients with BRCA (N = 302) and ATM (N = 103) alterations were randomized (ITT, N = 405). After an overall median follow-up of 44.0 months, median OS in the BRCA subgroup in the rucaparib arm was 23.2 months vs 21.2 months for the physician’s choice control arm (HR, 0.91 [95% CI, 0.68–1.20]; P = 0.5044; Table). Hierarchical testing did not continue due to lack of statistical significance. No OS benefit was observed in the ITT population or ATM subgroup (Table). Median duration of treatment in rucaparib and physician’s choice arms was 8.3 and 5.1 months, respectively. The most frequent any-grade treatment emergent adverse event (TEAE) in the rucaparib (n = 270) and physician’s choice (n = 130) arms was asthenia/fatigue (61.5% and 63.1%, respectively). The most frequent grade ≥3 TEAE was anemia (23.7%) with rucaparib, and asthenia/fatigue (9.2%) with physician’s choice. Of the 135 patients in the physician’s choice arm, 77 patients had radiographic progression and 70 crossed over to rucaparib. Conclusions: Rucaparib remains the only PARPi to show improved rPFS vs a DTX-containing control arm and has a similar OS even when most patients cross over to rucaparib. Safety was consistent with prior reports. These data support rucaparib as a treatment option for patients with BRCA-mutated mCRPC. Clinical trial information: NCT02975934 . Median OS at final analysis. Group Rucaparib, n Physician's choice, n Rucaparib, months Physician's choice, months HR (95% CI) a BRCA 201 101 23.2 21.2 0.91 (0.68–1.20) ITT 270 135 22.8 21.7 0.99 (0.78–1.26) ATM 69 34 18.4 22.1 1.21 (0.77–1.90) a Calculated by stratified Cox proportional hazard model.

121 Background: In the Phase 3 VISION trial, treatment with the prostate-specific membrane antigen (PSMA)-targeted radioligand therapy [ 177 Lu]Lu-PSMA-617 ( 177 Lu-PSMA-617) + protocol-permitted standard of care (SoC) significantly improved median radiographic progression-free survival (rPFS; 8.7 vs 3.4 months [mo]) and overall survival (OS; 15.3 vs 11.3 mo) in patients with metastatic castration-resistant prostate cancer (mCRPC) vs SoC alone. However, it is unclear how the addition of androgen receptor pathway inhibitors (ARPIs) affected 177 Lu-PSMA-617 treatment outcomes. Here we compared the efficacy and safety of 177 Lu-PSMA-617 in patients treated with vs without concomitant ARPIs. Methods: In VISION, adult patients with PSMA-positive mCRPC previously treated with ≥1 prior ARPI and 1–2 taxane chemotherapy regimens were randomized 2:1 to receive 177 Lu-PSMA-617 (7.4 GBq Q6W, 4–6 cycles) + SoC (which included ARPIs) vs SoC alone. In this secondary analysis, we assessed baseline characteristics, OS, rPFS, prostate-specific antigen (PSA) response rate, duration of PSA response, PSA-PFS, and safety among patients in the intervention arm who were treated with vs without concomitant ARPIs. Results: In total, 289 patients were treated with concomitant ARPIs and 262 patients were not (N=551). Imbalances between the groups were observed in some baseline characteristics: patients treated with concomitant ARPIs were younger, had lower ECOG performance scores, lower mean PSA and lactate dehydrogenase levels, and fewer prior taxane chemotherapy regimens. Baseline mean standardized [ 68 Ga]Ga-PSMA-11 uptake values and mean hemoglobin levels were well-balanced. A statistically significant difference in median OS was observed in patients treated with concomitant ARPIs vs those without (17.8 vs 12.4 mo; HR, 0.72; 95% CI, 0.58–0.89; nominal P=0.001). No statistically significant between-group differences were observed for rPFS, PSA response rate, duration of PSA response or PSA-PFS. The proportion of adverse events reported was similar in patients with or without concurrent ARPI, except for the number of adverse events leading to interruption of best supportive care/SoC, which was higher in patients treated with concurrent ARPIs. Conclusions: OS was significantly different in patients treated with concomitant ARPIs vs those without, while other efficacy endpoints were not. No new safety signals were observed for 177 Lu-PSMA-617 with concomitant ARPI. These findings may be confounded by varied exposure to ARPIs, or differing patient characteristics; patients who received concomitant ARPIs may represent a more favorable treatment population than those who did not. These findings should be considered as hypothesis-generating, and a multivariate analysis has been planned to ascertain the influence of these potential biases. Clinical trial information: NCT03511664 .

AbstractBackground[177Lu]Lu–PSMA‐617 (177Lu‐PSMA‐617) plus protocol‐permitted standard of care (SOC) prolonged overall survival (OS) and radiographic progression‐free survival (rPFS) versus SOC in patients with prostate‐specific membrane antigen (PSMA)–positive metastatic castration‐resistant prostate cancer (mCRPC) in the phase 3 VISION study, in addition to beneficial effects on symptomatic skeletal events (SSEs) and health‐related quality of life (HRQOL).MethodsPost hoc analyses used the full analysis set from the VISION study (N = 831) overall and by randomized treatment arm (177Lu‐PSMA‐617 plus SOC, n = 551; SOC, n = 280). Correlations were determined between OS and rPFS and between rPFS or OS and time to SSE or to worsening HRQOL (Functional Assessment of Cancer Therapy–Prostate [FACT‐P] and 5‐level EQ‐5D [EQ‐5D‐5L]). Correlation analyses used an iterative multiple imputation copula‐based approach (correlation coefficients [rho] of <0.3 were defined as weak, ≥0.3 and <0.5 as mild, ≥0.5 and <0.7 as moderate, and ≥0.7 as strong).ResultsIn the overall population, rPFS correlated strongly with OS (rho, ≥0.7). Correlations between rPFS or OS and time to SSE without death were weak or mild. Time to worsening in the FACT‐P total score and emotional and physical well‐being domains correlated mildly or moderately with rPFS and moderately with OS. Correlation coefficients for time‐to‐worsening EQ‐5D‐5L scores were mild to moderate for both rPFS and OS. Correlation coefficients were similar between treatment arms.ConclusionsIn this analysis of the VISION study, rPFS correlated strongly with OS but not with time to SSE or worsening HRQOL. These findings require further investigation.

5008 Background: [177Lu]Lu-PSMA-617 (177Lu-PSMA-617) prolonged radiographic progression-free survival (rPFS) versus androgen receptor pathway inhibitor (ARPI) change in taxane-naive patients with metastatic castration-resistant prostate cancer (mCRPC) in PSMAfore (NCT04689828). In this exploratory analysis, associations between baseline circulating tumor DNA (ctDNA) and outcomes were assessed. Methods: Patients were randomized 1:1 to 177Lu-PSMA-617 (7.4 GBq Q6W; 6 cycles) or ARPI change (abiraterone/enzalutamide). Patients known to have actionable mutations (e.g. BRCA) were excluded. The primary endpoint was rPFS. Baseline plasma ctDNA was analyzed using a customized 585-gene sequencing assay. ctDNA fraction was assessed in all samples passing quality control. Alterations in key prostate cancer drivers (prevalent in >10% participants) were assessed in samples with ctDNA fraction >1%. Univariate Cox regression (reference: ARPI change) was used to assess association of ctDNA fraction or alterations with rPFS, prostate-specific antigen response (≥50% decline; PSA50) and RECIST response (RR) at the June 21, 2023 data cutoff. Results: Of 360 samples from 468 patients, 255 passed quality control and 156 had ctDNA fraction >1% (median 5.85%; range 0–85). Detection of ctDNA alterations was comparable between arms and with published data. Median rPFS was shorter for patients with ctDNA fraction > versus ≤1% (HR 2.753; 95% CI 1.957–3.872; p<0.0001) (Table); ctDNA fraction >1% was also associated with worse RR and PSA50 response. Median rPFS was shorter for patients with detected versus undetected AR(HR 1.954; 95% CI 1.333–2.865; p<0.001), TP53(1.655; 1.13–2.426; p<0.01) and PTEN(1.62; 1.018–2.578; p<0.05) alterations. Median rPFS was longer with 177Lu-PSMA-617 versus ARPI change in patients with detected AR, TP53, PTEN(Table) , PI3K pathway and DNA repair pathway alterations. There was no significant association between ctDNA alterations and PSA50 or RR. Conclusions: ctDNA fraction >1% and AR, TP53and PTENalterations were associated with worse outcomes in PSMAfore regardless of treatment. Nonetheless, patients with these negative prognostic biomarkers did better with 177Lu-PSMA-617 than with ARPI change. Clinical trial information: NCT04689828 . [Table: see text]

5003 Background: [177Lu]Lu-PSMA-617 (177Lu-PSMA-617) prolonged radiographic progression-free survival vs change of androgen receptor pathway inhibitor (ARPI) in taxane-naïve patients with metastatic castration-resistant prostate cancer (mCRPC) in PSMAfore (NCT04689828). We now present health-related quality of life (HRQoL) and pain outcomes at second interim analysis. Methods: Eligible patients had mCRPC, were candidates for change of ARPI after progression on one prior ARPI, and had ≥1 PSMA-positive and no exclusionary PSMA-negative metastatic lesions by [68Ga]Ga-PSMA-11 PET/CT. Ineligible patients were candidates for PARP inhibition or had received prior systemic radiotherapy, immunotherapy or chemotherapy. Patients were randomized 1:1 to open-label 177Lu-PSMA-617 (7.4 GBq/6 weeks; 6 cycles) or ARPI change (abiraterone/enzalutamide). Patients with confirmed radiographic progression on ARPI change could cross over to 177Lu-PSMA-617. Secondary endpoints included time to worsening (TTW) in self-reported HRQoL (FACT-P, EQ-5D-5L) and pain (BPI-SF), defined as a composite of score worsening (prespecified thresholds), clinical progression (including new anti-cancer treatment) or death. Post hoc analyses of TTW in FACT-P and BPI-SF excluded clinical progression and death. The study was not powered for these endpoints and type I error was not controlled. Results: We randomized 468 patients (234/arm) with a median age of 72 years (range, 43–94). Median duration of exposure was 8.4 months for 177Lu-PSMA-617 and 6.5 months for ARPI change. 177Lu-PSMA-617 delayed TTW in FACT-P, EQ-5D-5L and BPI-SF scales and subscales vs ARPI change (Table). Results were similar in non-composite analyses. Incidence of grade ≥3 adverse events (AEs), serious AEs and AEs leading to discontinuation for 177Lu-PSMA-617 and ARPI change were 34% vs 44%, 20% vs 28% and 5.7% vs 5.2%, respectively. Conclusions: 177Lu-PSMA-617 delayed TTW in self-reported pain and HRQoL vs change of ARPI in taxane-naïve patients with PSMA-positive mCRPC. Clinical trial information: NCT04689828 . [Table: see text]

What is the role of pcRPLND in men with retroperitoneal vital cancer after first-line chemotherapy? This question arises because of the potential predictive value of miR371 in identifying residual cancer even before pcRPLND! @cdfankhauser shared data within a multicenter cohort study redefining future practice in the miR371 era.

18 Background: TRITON3 (NCT02975934) is a randomized, multicenter, open-label, phase 3 study of rucaparib vs physician’s choice (docetaxel [DTX], abiraterone [ABI] or enzalutamide [ENZ]) in patients (pts) with chemotherapy-naïve mCRPC with BRCA1/2 (BRCA) or ATM alterations. It was previously reported that rucaparib significantly improved the primary endpoint of radiographic progression-free survival (rPFS) vs physician’s choice in pts with BRCA or ATM alterations. We report here the interim overall survival (OS) and also report on efficacy of rucaparib compared individually with either DTX or ABI/ENZ. Methods: Pts had disease progression after 1 prior second-generation androgen pathway inhibitor therapy in any setting and were randomized 2:1 to rucaparib 600 mg BID or physician’s choice of DTX, ABI or ENZ. An ordered step-down multiple comparisons procedure was used to control the overall error rate. OS was a key secondary endpoint with rPFS as the primary endpoint tested first in the BRCA subgroup, then the intent-to-treat (ITT) population. Subgroup analyses based on physician’s choice were exploratory. Results: As of August 25, 2022, 302 pts with BRCA and 103 pts with ATM alterations were randomized. OS maturity was 54% in the BRCA subgroup and 59% in the ITT population. rPFS and OS are shown. The most frequent treatment-emergent adverse event (TEAE) in the rucaparib, DTX and ABI/ENZ groups was asthenia/fatigue (61.1%, 67.6% and 57.6%, respectively). The most frequent grade ≥3 TEAE in the rucaparib, DTX and ABI/ENZ groups was anemia (23.7%), neutropenia (14.1%), and hypertension (10.2%), respectively. Conclusions: Rucaparib significantly improved rPFS vs either DTX or ABI/ENZ; safety was consistent with prior reports. Interim OS results suggest a trend towards improvement for rucaparib vs DTX or ABI/ENZ in pts with mCRPC and BRCA alterations. Clinical trial information: NCT02975934 . [Table: see text]

5001 Background: In the phase 3 VISION trial, targeted radioligand therapy with lutetium (177Lu) vipivotide tetraxetan ([177Lu]Lu-PSMA-617; 177Lu-PSMA-617) significantly prolonged radiographic progression-free survival (rPFS) and overall survival (OS) when added to standard of care (SoC) in patients with advanced prostate-specific membrane antigen (PSMA) PET-positive metastatic castration-resistant prostate cancer. Benefits were consistent across most pre-specified subgroups. In this post hoc exploratory analysis, we examined rPFS and OS in the context of prior and concomitant cancer-directed treatments. Methods: In VISION, adult patients previously treated with at least 1 androgen receptor pathway inhibitor (ARPI) and 1–2 taxane regimens were randomized 2:1 to 177Lu-PSMA-617 (7.4 GBq Q6W, up to 6 cycles) + SoC or SoC alone. Protocol-permitted SoC excluded cytotoxic chemotherapy, systemic radioisotopes, immunotherapy, or other investigational drugs. Exploratory subgroup analyses of rPFS and OS were performed by: number of prior ARPIs; taxane regimens; non-taxane regimens and immunotherapies; prior treatment with bone-sparing agents; 223Ra and PARP inhibitors; and concomitant treatment with ARPIs, radiation therapy, and bone-sparing agents. Results: Prior and concomitant treatments were generally well balanced between study groups (Table). rPFS and OS benefits with 177Lu-PSMA-617 were consistent across all prior treatment subgroups. Notably, there were benefits in patients who had not received a second prior taxane. There were also consistent benefits regardless of concomitant systemic and radiation therapy as part of SoC. Conclusions: The clinical efficacy of 177Lu-PSMA-617 was observed regardless of prior treatment or SoC chosen, suggesting that disease biology rather than prior and concomitant treatment context drives outcomes. Small differences in outcomes between subgroups may warrant further study to understand better the predictors of improved clinical benefit. Clinical trial information: NCT03511664. [Table: see text]