Hussain, Arif

10610 Background: The role for genetic testing (GT) for prostate cancer (PCa) patients (pts) has expanded to find pts with germline pathogenic variants (PV) for therapeutic opportunities given FDA-approvals for PARP inhibitors in metastatic PCa as well as understanding familial cancer risk and opportunities for tailored screening and risk reduction. The PROMISE Registry (NCT04995198) was set up as a genetic registry to partner with PCa pts for rapid access to a new standard of care given insurance coverage and clinical implementation were initially major barriers. A second goal is to characterize disease features and treatment outcomes to inform management and provide updates about novel therapeutic clinical trials, both of which remain important to rare genetic variant carriers. Methods: PROMISE is a US decentralized prospective PCa genetic registry initiated in 2021 with initial phase to enroll and provide clinical-grade germline genetic testing (30 gene cancer-specific panel) to 5,000 PCa pts to identify ~500 PCa pts with variants of interest (pathogenic variants, PV, and variants of uncertain significance, VUS) in DNA repair genes for long-term clinical follow-up of 15 years (LTFU). Here, we report the initial phase testing results and identification of the LTFU cohort. Study design and enrollment strategy have been reported separately. Results: Between 2021-2026, 7,275 pts with any stage PCa across 50 US states self-consented to PROMISE, of which 5,674 (78%) of pts completed genetic testing, indicating feasibility of patient-directed, decentralized enrollment. We have identified 495 (8.7%) pts for LTFU. Baseline data is reported for n=367 (Table 1, will be updated at time of presentation). The most frequently observed PV/LPV variants being in CHEK2 (25%) , BRCA2 (23%) , ATM (12%) , and BRCA1 (4.6%). At the time of PCa diagnosis, the majority of LTFU pts had non-metastatic disease, with 47% of pts with Gleason>7, median PSA of 5 ng/mL, and median time from diagnosis to PROMISE GT of 25 months. Conclusions: PROMISE is a nationwide decentralized PCa genetic registry that has completed initial goal to recruit 5,000 PCa pts to offer germline genetic testing and recruit a cohort of 500 for LTFU. Data about diagnosis characteristics are reported, and analysis of ongoing disease course, treatment response/outcomes and overall survival is being collected. Clinical trial information: NCT04995198 . Long-term follow-up participant demographics. Characteristic Overall, N = 367 Age at Diagnosis (yrs) 63 (57, 69) Race N = 361 (6, nr) Asian, American Indian or Alaska Native, Multiracial, Other 22 (6.0%) Black or African American 22 (6.0%) White 317 (86%) Disease State at Diagnosis N = 348 (19, nr) Metastatic 46 (13%) Non-metastatic 302 (87%) Time from Diagnosis to PROMISE GT (months) 25 (4, 82) Gleason Score N = 280 (87, nr) </= 7 148 (53%) >7 132 (47%) PSA At Diagnosis (ng/mL) 5 (0, 10) (88, nr) Subjects with baseline data entered. nr=not reported. Median (Q1, Q3); n (%).

Abstract Purpose: The PARP inhibitor rucaparib is approved in the United States for patients with metastatic castration-resistant prostate cancer (mCRPC) and a deleterious germline and/or somatic BRCA1 or BRCA2 (BRCA) alteration. While sequencing of tumor tissue is considered the standard for identifying patients with BRCA alterations (BRCA+), plasma profiling may provide a minimally invasive option to select patients for rucaparib treatment. Here, we report clinical efficacy in patients with BRCA+ mCRPC identified through central plasma, central tissue, or local genomic testing and enrolled in TRITON2. Patients and Methods: Patients had progressed after next-generation androgen receptor–directed and taxane-based therapies for mCRPC and had BRCA alterations identified by central sequencing of plasma and/or tissue samples or local genomic testing. Concordance of plasma/tissue BRCA status and objective response rate and prostate-specific antigen (PSA) response rates were summarized. Results: TRITON2 enrolled 115 patients with BRCA+ identified by central plasma (n = 34), central tissue (n = 37), or local (n = 44) testing. Plasma/tissue concordance was determined in 38 patients with paired samples and was 47% in 19 patients with a somatic BRCA alteration. No statistically significant differences were observed between objective and PSA response rates to rucaparib across the 3 assay groups. Patients unable to provide tissue samples and tested solely by plasma assay responded at rates no different from patients identified as BRCA+ by tissue testing. Conclusions: Plasma, tissue, and local testing of mCRPC patients can be used to identify men with BRCA+ mCRPC who can benefit from treatment with the PARP inhibitor rucaparib.

BackgroundSystemic therapy (ST) can be deferred in patients who have metastatic renal cell carcinoma (mRCC) and slow‐growing metastases. Currently, this subset of patients managed with active surveillance (AS) is not well described in the literature.MethodsThis was a prospective observational study of patients with mRCC across 46 US community and academic centers. The objective was to describe baseline characteristics and demographics of patients with mRCC initially managed by AS, reasons for AS, and patient outcomes. Descriptive statistics were used to characterize demographics, baseline characteristics, and patient‐related outcomes. Wilcoxon 2‐sample rank‐sum tests and χ2 tests were used to assess differences between ST and AS cohorts in continuous and categorical variables, respectively. Kaplan‐Meier survival curves were used to assess survival.ResultsOf 504 patients, mRCC was initially managed by AS (n = 143) or ST (n = 305); 56 patients were excluded from the analysis. Disease was present in 69% of patients who received AS, whereas the remaining 31% had no evidence of disease. At data cutoff, 72 of 143 patients (50%) in the AS cohort had not received ST. The median overall survival was not reached (95% CI, 122 months to not estimable) in patients who received AS versus 30 months (95% CI, 25‐44 months) in those who received ST. Quality of life at baseline was significantly better in patients who were managed with AS versus ST.ConclusionsAS occurs frequently (32%) in real‐world clinical practice and appears to be a safe and appropriate alternative to immediate ST in selected patients.

AbstractBackgroundProstate‐specific membrane antigen (PSMA) is a well‐established therapeutic and diagnostic target overexpressed in both primary and metastatic prostate cancers. PSMA antibody‐drug conjugate (PSMA ADC) is a fully human immunoglobulin G1 anti‐PSMA monoclonal antibody conjugated to monomethylauristatin E, which binds to PSMA‐positive cells and induces cytotoxicity. In a phase 1 study, PSMA ADC was well tolerated and demonstrated activity as measured by reductions in serum prostate‐specific antigen (PSA) and circulating tumor cells (CTCs). To further assess PSMA ADC, we conducted a phase 2 trial in metastatic castration‐resistant prostate cancer (mCRPC) subjects who progressed following abiraterone/enzalutamide (abi/enz) therapy.MethodsA total of 119 (84 chemotherapy‐experienced and 35 chemotherapy‐naïve) subjects were administered PSMA ADC 2.5 or 2.3 mg/kg IV q3w for up to eight cycles. Antitumor activity (best percentage declines in PSA and CTCs from baseline and tumor responses through radiological imaging), exploratory biomarkers, and safety (monitoring of adverse events [AEs], clinical laboratory tests, and Eastern Cooperative Oncology Group performance status) were assessed.ResultsPSA declines ≥50% occurred in 14% of all treated (n = 113) and 21% of chemotherapy‐naïve subjects (n = 34). CTC declines ≥50% were seen in 78% of all treated (n = 77; number of subjects with ≥5 CTCs at baseline and a posttreatment result) and 89% of chemotherapy‐naïve subjects (n = 19); 47% of all treated and 53% of chemotherapy‐naïve subjects had a transition from ≥5 to less than 5 CTCs/7.5 mL blood at some point during the study. PSA and CTC reductions were associated with high PSMA expression (CTCs or tumor tissue) and low neuroendocrine serum markers. In the chemotherapy‐experienced group, the best overall radiologic response to PSMA ADC treatment was stable disease in 51 (60.7%) subjects; 5.7% of subjects in the chemotherapy‐naïve group had partial responses. The most common treatment‐related AEs ≥Common Terminology Criteria for AE (CTCAE) grade 3 were neutropenia, fatigue, electrolyte imbalance, anemia, and neuropathy. The most common serious AEs were dehydration, hyponatremia, febrile neutropenia, and constipation. Two subjects who received 2.5 mg/kg died of sepsis.ConclusionsPSMA ADC demonstrated some activity with respect to PSA declines, CTC conversions/reductions, and radiologic assessments in abi/enz treated mCRPC subjects. Clinically significant treatment‐related AEs included neutropenia and neuropathy.

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]

TPS388 Background: Up to 25% of patients with advanced prostate cancer, including mCRPC, have a deleterious germline or somatic mutation in BRCA1, BRCA2, ATM or another homologous recombination (HR) DNA repair gene that can serve as a molecular marker to select those who may respond to poly(ADP-ribose) polymerase inhibitors (PARPis). PARPis are lethal to cells with HRD, and PARPi treatment has shown preliminary evidence of an antitumor effect in patients with mCRPC who harbor a mutation in an HR DNA repair gene (Mateo et al. N Engl J Med. 2015;373:1697-708). These data provide a compelling rationale for evaluating rucaparib, a potent PARP1, PARP2 and PARP3 inhibitor, in patients with mCRPC associated with HRD. Methods: TRITON2 (NCT02952534) is a phase 2 study evaluating rucaparib 600 mg BID in patients with mCRPC. Patients with a deleterious germline or somatic BRCA1, BRCA2 or ATM mutation (per prior local test or central test during screening) will be enrolled into 1 of 2 cohorts based on the presence or absence of measurable visceral and/or nodal disease. An exploratory cohort will enroll patients with an alteration in any of 12 other prespecified HR genes (eg, RAD51C, RAD51D and PALB2), with or without measurable visceral and/or nodal disease. Patients must have progressed on androgen receptor signaling–directed therapy and 1 prior taxane-based chemotherapy for mCRPC. Patients who received prior treatment with a PARPi, mitoxantrone, cyclophosphamide or platinum-based chemotherapy are excluded. The primary endpoint is objective response rate measured using modified RECIST v1.1/PCWG3 for patients with soft-tissue disease and prostate-specific antigen response for patients with nonmeasurable disease. Secondary endpoints include duration of response, radiographic progression-free survival, overall survival, clinical benefit rate and safety. Pretreatment blood samples collected from all patients will enable development of a plasma-based companion diagnostic to select patients who may benefit from rucaparib treatment. Patients (≈160) will be enrolled at > 100 sites worldwide. Clinical trial information: NCT02952534.