Marshall, Catherine H.

PURPOSE The continuous development of new imaging approaches, molecular phenotyping, genetic subtypes, prognosis assessments, and effective therapies across a range of disease states has created a need to redefine terminology and best practices for clinical trial conduct in patients with advanced prostate cancer. Methods We convened an international expert committee of diverse working groups, the Prostate Cancer Working Group 4 (PCWG4), between 2016 and 2025. Our objective was to formulate updated criteria based on emerging evidence and clinical trial data in a biomarker context to provide guidance for clinical trial design, eligibility, and end point assessments for patients with advanced prostate cancer. RESULTS PCWG4 redefines terminology around the disease state and previous therapies in a patient-centric context and terminology focused on androgen pathway modulation. We consider imaging, with a particular focus on positron emission tomography (PET)–defined disease. New recommendations are provided for disease state terminology, defining eligibility criteria, response and delay/prevent end points, intervals for reassessments including imaging, and patient-reported outcome determination. We provide recommendations in a biomarker-based context of use for the intended indication, reflective of patient benefit for specific interventions. We emphasize the need for development of validated PET imaging and molecular and phenotypic criteria as well as trial designs to appropriately risk stratify patients, predict and assess benefit, and measure post-treatment outcomes reliably in a trial framework. CONCLUSION PCWG4 updates recommendations on patient and tumor characterization, therapy development, and imaging criteria and extends guidance into earlier androgen pathway modulator–naïve/sensitive disease states to reflect an evolving, heterogeneous, and diverse patient population to optimize treatment benefits for all patients.

PURPOSE Randomized clinical trials (RCTs) have shown progression-free survival (PFS) benefits of metastasis-directed therapy (MDT) without androgen deprivation therapy for oligometastatic castration-sensitive prostate cancer (omCSPC). Most patients with bone metastatic (BM) omCSPC recur with additional bone disease after MDT. We hypothesized the BM-targeting alpha-emitter radium-223 dichloride (Ra223) could target subclinical bone disease and delay progression. METHODS This is an investigator-initiated, multicenter, open-label phase II RCT. Eligible men with recurrent omCSPC with ≥one bone metastasis (≤three on conventional imaging and/or ≤five on molecular imaging) were randomly assigned (1:1) to stereotactic ablative radiation (SABR) MDT alone or SABR MDT with Ra223 (six cycles). Primary end point was composite PFS. RESULTS From August 9, 2019, to March 2, 2023, 64 patients were randomly assigned, 33 to SABR MDT and 31 to SABR MDT/Ra223 balancing for key covariates. Most SABR MDT/Ra223 patients (87%) received six cycles of Ra223. The median PFS was 11.8 months with SABR MDT and 10.5 months with SABR MDT/Ra223 (adjusted hazard ratio [aHR], 1.42 [95% CI, 0.79 to 2.56]; P = .24). Seven patients (11%) experienced grade 3 treatment-related adverse events (no grade 4 or 5), 2 of 33 (6%) with SABR and 5 of 30 (17%) with SABR MDT/Ra223. Patients with high-risk (HiRi) pathogenic mutations in ATM , BRCA1/2 , RB1 , or TP53 had worse PFS (HR, 5.95 [95% CI, 1.83 to 19.3]; P = .003). Greater T-cell receptor (TCR) unique productive rearrangements were prognostic for improved PFS independent of the treatment arm (aHR, 0.45 [95% CI, 0.21 to 0.96]; P = .04). CONCLUSION Adding Ra223 to SABR MDT in BM omCSPC does not delay progression of disease. We provide evidence for an HiRi mutational signature and TCR repertoire as prognostic biomarkers in omCSPC treated with SABR MDT, highlighting the importance of collecting biological correlates in RCTs for omCSPC.

Abstract Purpose: Germline alterations in homologous recombination repair (gHRR) genes affect the pathogenesis, treatment options, and survival of patients with cancer. However, distinct gHRR gene alterations may differentially affect treatment response and oncogenic signaling. In this study, we interrogated genomic and transcriptomic data and assessed clinical outcomes of patients with gHRR mutations across four BRCA-associated cancers (breast, ovarian, pancreatic, and prostate cancers) to identify therapeutic vulnerabilities. Experimental Design: We assessed 24,309 patients undergoing matched tumor/normal next-generation DNA and RNA sequencing. Annotated gHRR gene variants [germline BRCA1, germline BRCA2, germline PALB2, germline ATM (gATM), and germline CHEK2] were analyzed. HRs were used to assess survival outcomes comparing germline versus sporadic groups. Somatic alterations and their frequencies were compared across gHRR-altered groups. Differential gene expression and gene set enrichment analysis were used to compare transcriptomic profiles. Results: Somatic TP53 mutations were depleted in gATM carriers (P < 0.05) across all four BRCA-associated cancers by up to 2.5-fold. Tumors with germline BRCA1/2 mutations were associated with improved survival in patients with ovarian cancer and had consistent enrichment of TP53 mutations in all four cancers. gATM mutations displayed elevated p53 transcriptional activity in all four cancers, with significance reached in breast and prostate cancers (P < 0.01). In breast, ovarian, and prostate cancers, gATM tumors demonstrated significantly increased inflammatory pathways (P < 0.001). Finally, using gene dependency data, we found that cell lines that were highly dependent on ATM were co-dependent on canonical p53 function. Conclusions: gATM-associated cancers seem to require intact p53 activity and this synthetic essentiality may be used to guide targeted therapies that perturb canonical TP53 function.

202 Background: While several PARP inhibitors are approved in combination with hormonal therapies for metastatic castrate resistant prostate cancer (CRPC), their use in castrate sensitive prostate cancer (CSPC) is understudied. We previously reported that olaparib monotherapy (without ADT) shows significant clinical activity in BRCA2 -altered patients with biochemically recurrent (BCR) prostate cancer. Here, we explored prognostic and predictive PARP-related mRNA biomarkers derived from primary prostate tumors. Methods: We characterized the expression of 16 PARP transcripts using a cohort of 52,266 radical prostatectomy (RP) specimens (2016-2024) undergoing Decipher prostate genomic classifier testing (Veracyte Inc). Transcriptome-wide mRNA expression data as well as baseline clinical/pathologic factors were retrieved from the Decipher GRID database (NCT02609269). Associations between high PARP expression (top 25%), baseline factors, and gene signatures were examined using logistic regression. We assessed the association between PARP expression and distant metastases in 3 retrospective cohorts (n= 545, 855, and 325). Finally, we evaluated PARP expression in our prior phase II trial (NCT03047135, n=39) of olaparib monotherapy in the setting of BCR following RP. Results: Higher mRNA levels of PARP1 , 2 , 8 and 14 showed strong associations (all P <0.001) with known adverse prognostic factors such as very-high Decipher score (>0.85), high Gleason grade (GG5) and non-organ confined disease (EPE, SVI and LNI), while higher PARP6 and 7 expression were associated with more favorable disease characteristics. High PARP1 expression was positively correlated with DNA-repair deficiency (r=0.77) and tumor immune microenvironment (r=0.62) signatures. In 3 independent retrospective cohorts of intermediate-high risk PCa patients, higher PARP1 expression was strongly associated with development of distant metastases after RP (HR 1.70, 1.81, and 1.67 respectively; all P <0.05). Finally, in our phase II trial of patients with BCR who received olaparib monotherapy, PARP1 (but not PARP2 ) expression from RP was 1.5-fold higher in samples with BRCA2 mutations (median 0.416 vs 0.276, P =0.01) and was associated with overall improved PSA progression-free survival (continuous variable, HR 0.55, P =0.01) and longer time to next systemic treatment (continuous variable, HR 0.66, P =0.02). Conclusions: High PARP1 mRNA expression, measured at RP, is associated with aggressive disease biology and greater risk of metastasis. However, high PARP1 (but not PARP2 ) levels are associated with improved response to PARP inhibition in the setting of BCR prostate cancer. Future trials testing PARP (including PARP1-selective) inhibitors in the CSPC space should consider measuring PARP1 mRNA levels in addition to BRCA1/2 mutation status. Clinical trial information: NCT02609269 , NCT03047135 .

199 Background: Contained within the spectrum of metastatic cancer is an oligometastatic state where metastases are limited in number. Recent prospective data have shown that metastasis directed therapy (MDT) can alter the natural history of oligometastatic disease. In hormone-sensitive prostate cancer (HSPC), the positive clinical effect of MDT has been observed by the phase II STOMP and ORIOLE trials. Circulating tumor cells (CTCs) are a likely origin of the formation of macroscopic metastases. CTCs thus may provide an approach for identifying subgroups of patients with oligometastatic HSPC (oligoHSPC) that would benefit most from MDT. Our main goal was to evaluate the association between presence of CTCs at baseline or day 180 with clinical outcomes in the ORIOLE trial. Methods: ORIOLE was a phase II trial randomizing men with recurrent oligoHSPC with 1-3 metastases to observation (Obs) versus stereotactic ablative radiotherapy (SABR) MDT. Blood samples were prospectively collected at baseline and day 180. Progression-free survival (PFS) was a composite endpoint including any of the following: a PSA rise of at least 2 ng/dL and 25% above nadir; radiologic progression by CT, MRI or bone scan (RECIST v1.1); symptomatic progression of disease; initiation of ADT; or death. Patient blood samples were shipped for analysis on Epic Sciences liquid biopsy platform (Epic Sciences, San Diego, CA). Machine learning algorithms identified CTCs and characterized androgen receptor (AR) expression. Comparisons of patient and tumor characteristics between the groups were performed by two-sample t-tests. Survival curves were generated using the Kaplan-Meier method and p-values were calculated using log-rank test. Analysis was performed using SPSS version 28. Results: A total of 82 samples were collected: 70 from the SABR arm (35 baseline and 35 on day 180) and 12 Obs (7 baseline and 5 on day 180). CTCs were detected in 30/42 samples at baseline (71%, AR+= 7) and in 26/40 samples on day 180 (65%, AR+= 9). In the SABR group there was no difference between CTC+ versus CTC- and AR + versus AR- groups for PSA evaluated at baseline, day 90 or day 180 or Gleason score. With a median follow-up of 41.7 months, PFS was significantly lower in the patients with AR+ versus AR- CTCs at baseline in the SABR arm (p = 0.011, mean PFS: AR+ = 9.3 months, AR- = 27.1 months). The mean biochemical failure-free survival was AR+= 12.9 versus AR-= 29.2 months (p = 0.058). Conclusions: Our preliminary results demonstrate an association between AR+ CTCs at baseline and Day 180 with clinical outcomes following SABR MDT in oligoHSPC. This is the first report examining baseline and dynamic presence of CTCs in oligoHSPC treated from a prospective randomized trial of SABR. Longer follow-up, further analysis and a greater number of patients are needed for a more comprehensive conclusion.

PURPOSE Two poly (ADP-ribose) polymerase (PARP) inhibitors (olaparib and rucaparib) are US Food and Drug Administration–approved for patients with metastatic castration-resistant prostate cancer (mCRPC) harboring BRCA1/ 2 mutations, but the relative efficacy of PARP inhibition in BRCA1- versus BRCA2-altered mCRPC is understudied. METHODS We conducted a multicenter retrospective analysis involving 12 sites. We collected genomic and clinical data from 123 patients with BRCA1/ 2-altered mCRPC who were treated with PARP inhibitors. The primary efficacy end point was the prostate-specific antigen (PSA) response (≥ 50% PSA decline) rate. Secondary end points were PSA progression-free survival (PSA-PFS), clinical or radiographic PFS, and overall survival. We compared clinical outcomes, and other genomic characteristics, among BRCA1- versus BRCA2-altered mCRPC. RESULTS A total of 123 patients (13 BRCA1 and 110 BRCA2) were included. PARP inhibitors used were olaparib (n = 116), rucaparib (n = 3), talazoparib (n = 2), and veliparib (n = 2). At diagnosis, 72% of patients had Gleason 8-10 disease. BRCA1 patients were more likely to have metastatic disease at presentation (69% v 37%; P = .04). Age, baseline PSA, metastatic distribution, and types of previous systemic therapies were similar between groups. There were equal proportions of germline mutations (51% v 46%; P = .78) in both groups. BRCA1 patients had more monoallelic (56% v 41%; P = .49) and concurrent TP53 (55% v 36%; P = .32) mutations. PSA 50 responses in BRCA1- versus BRCA2-altered patients were 23% versus 63%, respectively ( P = .01). BRCA2 patients achieved longer PSA-PFS (HR, 1.94; 95% CI, 0.92 to 4.09; P = .08), PFS (HR, 2.08; 95% CI, 0.99 to 4.40; P = .05), and overall survival (HR, 3.01; 95% CI, 1.32 to 6.83; P = .008). Biallelic (compared with monoallelic) mutations, truncating (compared with missense) mutations, and absence of a concurrent TP53 mutation were associated with PARP inhibitor sensitivity. CONCLUSION PARP inhibitor efficacy is diminished in BRCA1- versus BRCA2-altered mCRPC. This is not due to an imbalance in germline mutations but might be related to more monoallelic mutations and/or concurrent TP53 alterations in the BRCA1 group.

100 Background: Two PARP inhibitors (olaparib, rucaparib) are now FDA approved for mCRPC patients with mutations in BRCA1/2, but the relative efficacy of PARP inhibition in BRCA1- vs BRCA2-altered mCRPC is understudied. Methods: We conducted a multi-center retrospective analysis involving 11 academic sites. We collected genomic and clinical data from 123 BRCA1/2-altered mCRPC patients receiving PARP inhibitor treatment. The primary efficacy endpoint was PSA50 response rate (≥50% decline in PSA level). Secondary endpoints were PFS (clinical, radiographic or PSA progression, whichever occurred first) and overall survival (OS). We also captured information on other concurrent genomic alterations. We compared genomic characteristics and clinical outcomes among BRCA1- vs BRCA2-altered mCRPC. Results: A total of 123 patients (13 BRCA1, 110 BRCA2) were included. PARP inhibitors used were olaparib (n = 116), rucaparib (n = 3), talazoparib (n = 2) and veliparib (n = 2). All BRCA1 and 71% of BRCA2 patients had Gleason 8-10 disease. Compared to BRCA2 patients, BRCA1 patients were more likely to have received prior taxane chemotherapy (77% vs 62%). Age, baseline PSA, and prior enzalutamide/abiraterone treatment were similar between groups. PSA50 responses in BRCA1- vs BRCA2-altered patients were 38% vs 65% respectively ( P= 0.06). Median PFS in BRCA1 vs BRCA2 patients was 3.0 mo (95%CI, 0.9–5.1) vs 8.0 mo (95%CI, 5.3–10.6) respectively (HR 0.42, P= 0.01). Similarly, median OS in BRCA1 vs BRCA2 patients was 11.0 mo (95%CI, 9.9–12.1) vs 24.0 mo (95%CI, 18.2–29.8) respectively (HR 0.33, P= 0.005). There were roughly equal proportions of germline mutations (50% vs 45%) and biallelic mutations (31% vs 25%) in the BRCA2 and BRCA1 groups, respectively. There were numerically more TP53 mutations in the BRCA1 vs BRCA2 group (40% vs 29%, P= 0.45), but an equal number of mutations in other key genes ( PTEN, RB1 and AR). Conclusions: PARP inhibitor activity is diminished in BRCA1- vs BRCA2-altered mCRPC. In our cohort, this differential activity was not explained by mutation origin (germline vs somatic) or allelic status (mono- vs biallelic). These findings warrant validation.

154 Background: Poly ADP-ribose polymerase inhibitors (PARPi) are being studied as a treatment option for men with mCRPC and deficient homologous recombination DNA repair. While the FDA has granted “breakthrough” designation status to olaparib for use in mCRPC patients with either BRCA1/2 or ATM mutations, it is not known if responsiveness to PARPi may be influenced by the mutation type. Because ATM functions as a sensor of DNA damage rather than a mediator of DNA repair, we hypothesized that patients with ATM mutations may not show robust responses to PARPi therapy compared to those with BRCA1/2 mutations. Methods: We conducted a retrospective analysis of mCRPC patients treated with off-label olaparib at Johns Hopkins Hospital and Mayo Clinic Scottsdale who had somatic or germline mutations in BRCA1/ 2 or ATM. The primary endpoint was PSA50 response. Secondary endpoints included overall survival (OS) and radiographic/clinical progression-free survival (PFS). Results: 40 men received olaparib for mCRPC of which 17 had pathogenic mutations (5 ATM-mutant, 12 BRCA1/2-mutant). Eleven (65%) had germline and 6 (35%) had somatic alterations. Five (29%) had Gleason sum ≤7 at diagnosis, 4 (24%) had Gleason sum 8, and 8 (47%) had Gleason sum ≥9. Three (18%) had metastatic disease at diagnosis. Mean age at start of olaparib therapy was 65.6 (range, 52-76) years. Prior chemotherapy was received by 59% of men, and prior abiraterone/enzalutamide by 88% of men. Eleven (65%) had extra-osseous metastases at start of therapy. PSA50 responses were achieved by 10/12 men (83%) with BRCA1/2 mutations and 0/5 men (0%) with ATM mutations (Fisher’s exact test, P= 0.003). Men with BRCA1/2 mutations had a median PFS of 12.3 mo versus 3.3 mo for those with ATM mutations (HR 0.14, 95%CI 0.03-0.60; P= 0.008). There was no difference in OS (HR 0.24, 95%CI 0.03-1.173; P= 0.16). Conclusions: Men with mCRPC harboring mutations in BRCA1/2 appear to have better PSA responses and longer PFS with olaparib compared to men with ATM mutations. ATM-mutant mCRPC patients may require alternative therapies ( e.g. chemotherapy, ATR inhibitors). Larger prospective studies are needed to confirm or refute these preliminary findings.