Scher, Howard I.

162 Background: Clinical trial conduct in advanced prostate cancer has changed dramatically with the continued development of new imaging approaches, molecular phenotypes and genetic subtypes, prognosis assessments, and effective therapies across a range of disease states. This created a need to redefine terminology and best practices for clinical trials. Methods: We convened PCWG4, an international expert committee of multidisciplinary working groups, between 2016 and 2025 to update and expand PCWG2-3 recommendations based on emerging evidence and clinical trial data in an innovative biomarker and imaging context to provide guidance for clinical trial design, eligibility, and endpoint assessments. Results: PCWG4 redefines terminology around disease states and prior therapies in a patient-centric context, considering imaging modalities, with a particular focus on PET-defined disease. New recommendations are provided for disease state terminology, defining eligibility criteria, imaging and non-imaging-based responses. We define delay/prevent endpoints including responses by pathology, ctDNA, circulating tumor cells, and PSA declines, and specify intervals for re-assessments including imaging, biomarker assessments, and patient reported outcomes. We propose new imaging-specific rPFS criteria including guidance with serial PSMA PET/CT imaging (Table). We provide recommendations in a biomarker-based context for the 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. Conclusions: PCWG4 expands guidance on patient and tumor profiling, as well as therapy development, to include both androgen deprivation therapy sensitive and resistant settings, reflecting today’s more heterogeneous and diverse patient population to optimize outcomes. PCWG4-defined radiographic progression by imaging modality for patients with metastatic disease. Pretreatment Scan On-treatment Scan #1(≥week 8) On-treatment Scan #2 All Subsequent Scans Bone scintigraphy Comparator Comparator for subsequent scansPOD never called here POD:PCWG3 criteria (2+2 additional new lesions) POD:≤5 new lesions: PCWG3 criteria 2 new lesions confirmed≥6 new lesions CT/MRI Any measurable disease Comparator PCWG3/RECIST PCWG3/RECIST PCWG3/RECIST PSMA PET Bones, and lymph nodes and lung metastases (non-RECIST qualifying by + on PET only) Comparator POD:≤5 new lesions: 2 new lesions confirmed on a subsequent scan≥6 new lesions Same as prior Same as prior Liver and non-pulmonary viscera Comparator POD:Any single new lesion that represents disease Same as prior Same as prior

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.

Background: Management strategies for metastatic castration-resistant prostate cancer (mCRPC) have rapidly shifted in recent years. As novel imaging and therapeutic approaches have made their way to the clinic, providers are encountering increasingly challenging clinical scenarios, with limited guidance from the current literature. Materials and Methods: The US Prostate Cancer Conference (USPCC) is a multidisciplinary meeting of prostate cancer experts intended to address the many challenges of prostate cancer management. At the first annual USPCC meeting, areas of controversy and consensus were identified during a 2-day meeting that included expert presentations, full-panel discussions, and postdiscussion responses to questions developed by the USPCC cochairs and session moderators. Results: This narrative review covers the USPCC expert discussion and perspectives relevant to mCRPC, including neuroendocrine/aggressive-variant prostate cancer (NEPC/AVPC). Areas of broad agreement identified among USPCC experts include the benefits of poly (ADP-ribose) polymerase (PARP) inhibitors for patients with BRCA1/2 mutations, the use of radioligand therapy in patients with prostate-specific membrane antigen (PSMA)–positive mCRPC, and the need for clinical trials that address real-world clinical questions, including the performance of novel therapies when compared with modern standard-of-care treatment. Ongoing areas of controversy and uncertainty included the appropriateness of PARP inhibitors in patients with non-BRCA1/2 mutations, the optimal definition of PSMA positivity, and systemic therapies for patients with NEPC/AVPC after progression on platinum-based therapies. Conclusions: The first annual USPCC meeting identified several areas of controversy in the management of mCRPC, highlighting the urgent need for clinical trials designed to facilitate treatment selection and sequencing in this heterogeneous disease state.

Purpose: Castration-sensitive prostate cancer (CSPC) is a complex and heterogeneous condition encompassing a range of clinical presentations. As new approaches have expanded management options, clinicians are left with myriad questions and controversies regarding the optimal individualized management of CSPC. Materials and Methods: The US Prostate Cancer Conference (USPCC) multidisciplinary panel was assembled to address the challenges of prostate cancer management. The first annual USPCC meeting included experts in urology, medical oncology, radiation oncology, and nuclear medicine. USPCC co-chairs and session moderators identified key areas of controversy and uncertainty in prostate cancer management and organized the sessions with multidisciplinary presentations and discussion. Throughout the meeting, experts responded to questions prepared by chairs and moderators to identify areas of agreement and controversy. Results: The USPCC panel discussion and question responses for CSPC-related topics are presented. Key advances in CSPC management endorsed by USPCC experts included the development and clinical utilization of gene expression classifiers and artificial intelligence (AI) models for risk stratification and treatment selection in specific patient populations, the use of advanced imaging modalities in patients with clinically localized unfavorable intermediate or high-risk disease and those with biochemical recurrence, recommendations of doublet or triplet therapy for metastatic CSPC (mCSPC), and consideration of prostate and/or metastasis-directed radiation therapy in select patients with mCSPC. Conclusions: CSPC is a diverse disease with many therapeutic options and the potential for adverse outcomes associated with either undertreatment or overtreatment. Future studies are needed to validate and clinically integrate novel technologies, including genomics, AI, and advanced imaging, to optimize outcomes among patients with CSPC.

TPS292 Background: PT-112 is a novel small I-O molecule currently in development for several cancers. Preclinical studies have shown the robust induction of immunogenic cell death by PT-112, leading to an anti-cancer adaptive immune response. Biodistribution experiments in mice showed PT-112’s partial bone affinity. In two prior phase I studies, late-line metastatic castration-resistant prostate cancer patients (mCRPC pts) were treated with evidence of anti-cancer activity, including tumor volume reductions, improvements in PET and bone scans, PSA and alkaline phosphatase (ALP) reductions, and anecdotal cases of improvement in disease-related pain. This, taken together with the immunogenic and osteotropic properties observed in preclinical work, provided a strong rationale to further explore PT-112 in mCRPC, an immunologically “cold” disease with a high prevalence of bone metastases. Moreover, in an analysis of >6,000 mCRPC pts, circulating tumor cell (CTC) declines (CTC0 and CTC conversions) were correlated with improvements in survival to a greater extent than PSA declines (PSA50) (Heller et al., JCO, 36:6 2017), prompting incorporation of CTC changes as a secondary endpoint. Methods: The primary objective of the study is to define the dose regimen of PT-112 for pivotal study. Pts are randomized to one of three arms, receiving IV PT-112 on 28-day cycles via one hour infusions on (1) Days 1 and 15 at 250 mg/m2, (2) Days 1 and 15 at 360 mg/m2, or (3) Days 1 and 15 of cycle 1 at 360 mg/m2 followed by 250 mg/m2 on Day 15 of subsequent cycles. Key eligibility criteria include radiographically progressive disease at study entry; ≥3 life-prolonging therapies for metastatic disease including 1-2 taxanes, ≥1 new generation anti-androgen therapies, and other drugs FDA approved on the basis of survival; and allowing bone-only metastatic disease. Efficacy assessments comprise disease control rate at 4 months (DCR4) using RECIST and PCWG3 criteria, objective response rate, CTC0 and CTC conversion, PSA50 and ALP reductions. Additionally, T cell receptor sequencing is conducted to characterize treatment-induced changes in T cell fraction and clonal expansions, as a means of generating meaningful supportive data on the immune mechanism of PT-112 monotherapy. A Fleming two-stage design will be used to assess each arm, with a 20% DCR4 as the null hypotheses, requiring ≥6 of 25 pts responding in stage one and ≥14 of 45 in total to reject the null. In addition, other efficacy measures, such as CTC responses, as well as exposure/response and exposure/safety analyses will be applied to characterize the risk/benefit ratio and select the optimal dose regimen for PT-112. As of October 11th, 2022, 38 pts have been enrolled out of a planned maximum of 135. Clinical trial information: NCT02266745 .

5038 Background: Platinum-based chemotherapy has shown palliative and radiographic benefit in small unselected studies of metastatic castration-resistant prostate cancer (mCRPC). Alterations in DNA damage repair genes (DDRmut), which occur in ~25% of patients with mCRPC, may sensitize to platinum-based chemotherapy, and may aid in the selection of patients for this therapy. We sought to evaluate the efficacy of platinum-based chemotherapy in DDRmut mCRPC. Methods: We performed a retrospective review of patients with prostate cancer who underwent tumor genomic profiling and received platinum-based chemotherapy. Deleterious alterations in a panel including BRCA2, BRCA1, ATM, FANCA, CDK12 or PALB2 were classified as DDRmut. Absence of deleterious alterations in those genes was classified as DDRwt. MSI-H cases were excluded from analysis. Electronic charts, PSA values, and scans were reviewed to assess for outcomes. Results: From October 2013 to July 2018, 109 patients with mCRPC received platinum-based chemotherapy. 64/109 had prior taxane progression and were PARP inhibitor (PARPi) naïve at the time of platinum-based chemotherapy. DDRmut was found in 16/64 (25%) of patients ( BRCA2, n = 6; ATM, n = 2; CDK12, n = 4; FANCA, n = 4; PALB2, n = 1). Visceral metastasis occurred in 4/16 (25%) of DDRmut patients and in 22/48 (46%) of DDRwt patients. PSA50 responses were more common among DDRmut (8/15 evaluable = 53%, 95% CI, 30-75%) than among DDRwt patients (5/42 evaluable = 12%, 95% CI, 5-25%). Time on platinum-based chemotherapy tended to be longer in the DDRmut group (median 3.1 vs 1.8 months; HR 0.73, 95% CI 0.42-1.26). Of 8 DDRmut patients ( BRCA2, n = 6; BRCA1, n = 1; ATM, n = 2) who received platinum-based chemotherapy after progression on a PARPi, 3/7 evaluable patients (43%) had RECIST response or stable disease, and 2/7 evaluable patients (29%) had a PSA50 response. Of 4 patients with ATM deleterious mutations, none had a radiographic or PSA50 response to platinum-based chemotherapy. Conclusions: Platinum-based chemotherapy showed activity in DDRmut mCRPC patients before and after PARPi treatment.

5031 Background: The phase 2 TRITON2 study (NCT02952534) is evaluating the PARP inhibitor rucaparib in patients with mCRPC who have a deleterious germline or somatic alteration in BRCA ( BRCA1 or BRCA2) or 1 of 13 other DNA damage repair genes. Here we present analyses of tumor genomics and baseline clinical characteristics in mCRPC patients with a deleterious alteration in BRCA. Methods: Plasma (baseline) and tissue (archival or baseline) samples from patients with a deleterious alteration in BRCA were analyzed using Foundation Medicine next-generation sequencing assays. The alterations and zygosity of the alterations that were detected, as well as the somatic/germline status from Color Genomics testing, were summarized. Associations between genomic alterations, DNA yield, allele frequency, and baseline clinical characteristics were investigated. Results: Results are shown in the Table for a cohort of 40 BRCA2 and 5 BRCA1 patients enrolled in TRITON2 (Abida W et al. Presented at ESMO 2018. Abst 793PD). A biallelic alteration was observed in 21 of the 22 BRCA2 patients (95%) for whom alteration zygosity could be determined. Among the 5 BRCA1 patients, 1 alteration was monoallelic and 4 were of unknown zygosity. Co-occurring alterations in cancer-related or DNA damage repair genes were observed in many patients with BRCA alterations. At baseline, cell-free DNA (cfDNA) yield correlated positively with the sum of target lesions (STL; P= 0.04), but not with prostate-specific antigen (PSA) levels ( P= 0.86). No correlation was observed between allele frequency of the BRCA alteration baseline STL ( P= 0.68) or PSA levels ( P= 0.97). Conclusions: Patients with a BRCA mutation enrolled in TRITON2 demonstrate a profile of genomic alterations consistent with that of prior studies of patients with mCRPC. Plasma cfDNA profiling showed a correlation between baseline cfDNA yield and measurable tumor burden, but not baseline PSA. Clinical trial information: NCT02952534. [Table: see text]

5045 Background: Trophoblastic cell-surface antigen (Trop-2) is a transmembrane glycoprotein that is highly expressed in many solid tumors. Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate of an anti-Trop-2 humanized antibody with SN-38. Early clinical trials have shown high response rates in a broad range of diseases including triple negative breast and urothelial cancers. We evaluated Trop-2 expression in tumor biopsies and circulating tumor cells (CTCs) from men with mCRPC (metastatic castrate-resistant prostate cancer). Methods: Trop-2 expression was evaluated from mCRPC biopsies from patients (Pts) treated with abiraterone acetate (AA) on the PROMOTE clinical trial, CTCs from a separate cohort treated with either enzalutamide or AA. Trop-2 CTCs were compared with EpCAM captured CTCs using a microscale technology termed the VERSA (Vertical Exclusion-based Rare Sample Analysis) platform to compare protein and gene expression signatures of resistance to these agents. Results: RNA sequencing identified Trop-2 gene expression in > 70% of metastatic biopsies. The AR splice variant V7 was found in 48 biopsies that also expressed Trop-2. Trop-2 expression was not altered by treatment with AA at 12 weeks. The number of CTCs captured from 25 pts with Trop-2 or EpCAM were closely correlated (R2= 0.84). Gene expression analysis showed similar patterns of expression for the TROP-2 and EPCAM captured cells. AR splice variant expression (AR-V7, AR-V9) in Trop-2 and EpCAM CTCs was detected in 33% of patients. Expression of neuroendocrine markers was identified in 40% of Trop-2 CTCs. Conclusions: Trop-2 is frequently expressed in mCRPC and co-expressed in tumors that express AR splice variants. Trop-2 CTCs are detected in CRPC pts previously treated with AA or Enzalutamide that also express multiple AR splice variants and neuroendocrine markers. The results support Trop-2 expression as predictive biomarker of sensitivity to targeted therapies tumors resistant to AA or Enzalutamide. Men with mCRPC are being enrolled on a Phase I trial with IMMU-132, and multi-site Phase II clinical trial in men who have progressed on AA or Enzalutamide is being finalized.

LBA2 The full, final text of this abstract will be available at abstracts.asco.org at 7:30 AM (EDT) on Sunday, June 4, 2017, and in the Annual Meeting Proceedings online supplement to the June 20, 2017, issue of the Journal of Clinical Oncology. Onsite at the Meeting, this abstract will be printed in the Sunday edition of ASCO Daily News.