Citations

Abstract Purpose: Mutations in hematopoietic progenitor cells accumulate with age leading to clonal expansion, termed clonal hematopoiesis (CH). CH in the general population is associated with hematopoietic neoplasms and reduced overall survival (OS), predominantly through cardiovascular adverse events (CVAE). Because androgen receptor pathway inhibitors (ARPI) used in metastatic castration-resistant prostate cancer (mCRPC) are also associated with CVAEs and because CH negatively impacted survival in an advanced solid tumor cohort, we hypothesized that CH in mCRPC may be associated with increased CVAEs and inferior survival. Experimental Design: A targeted DNA sequencing panel captured common CH mutations in pretreatment blood samples from 957 patients enrolled in Alliance A031201: a randomized trial of enzalutamide ± abiraterone/prednisone in the first-line mCRPC setting. The primary outcome was the impact of CH on OS; the secondary outcomes were progression-free survival (PFS) and CVAEs. Results: Baseline comorbidities were similar by CH status. No differences in OS/progression-free survival were detected regardless of treatment arm or the variant allele frequency threshold used to define CH [primary: 2% (normal-CH, N-CH); exploratory: 0.5% (low-CH) and 10% (high-CH, H-CH)]. Patients with H-CH (7.2%) and TET2-mutated N-CH (6.0%) had greater odds of any CVAE (14.5% vs. 4.0%; P = 0.0004 and 12.3% vs. 4.2%; P = 0.010, respectively). More major CVAEs were observed in patients with H-CH (5.8% vs. 1.9%; P = 0.042) and N-CH (3.4% vs. 1.8%; P = 0.147). Conclusions: CH did not affect survival in patients with mCRPC treated with ARPIs in A031201. H-CH and TET2-mutated CH were associated with more CVAEs. These findings inform the risk/benefit discussion about ARPIs in mCRPC.

TPS5118 Background: Novel androgen receptor pathway inhibitors (ARPIs) improve overall survival (OS) in patients (pts) with metastatic hormone-sensitive prostate cancer (mHSPC) in conjunction with testosterone suppression (TS) relative to TS alone. However, the duration of treatment required to derive clinical benefit is unclear, as is whether continuous treatment is requisite for optimal cancer outcomes. Favorable PSA declines have been associated with prolonged OS in clinical trials testing TS + ARPIs. We thus designed this single-arm Phase 2 trial to test the hypothesis that pts who achieve exceptional response to upfront TS + ARPI can suspend treatment, allowing for T recovery and improvement in quality of life while maintaining favorable clinical outcomes. Methods: Eligible pts had mHSPC by conventional imaging with PSA ≥ 5 ng/ml and T ≥ 150 ng/dl (or not known to have been hypogonadal) prior to starting treatment, have been receiving TS for 540-750 days and ARPI for ≥ 360 days, and have achieved PSA < 0.2 ng/ml (stable or falling for 3 consecutive measurements) with castrate T <50 ng/dl at the time of enrollment. Intermittent ADT for biochemical recurrence prior to mHSPC diagnosis, prior local therapy, prior radiation to metastatic sites, and up to 6 cycles of docetaxel in mHSPC are permitted. Pts who underwent surgical castration, received ARPI prior to mHSPC diagnosis, or are receiving experimental treatment for mHSPC or participating in a clinical trial that does not allow for TS or ARPI interruption are excluded. After enrollment, pts discontinue both TS and ARPI and are followed with PSA and T levels every 3 months, conventional CT/MRI and bone scan at least every 6 months, and FACT-P questionnaire for patient-reported outcomes every 6 months. Treatment re-initiation triggers are PSA increase to ≥ 5 ng/ml, radiographic change (progressive disease per modified RECIST 1.1 on CT/MRI or unconfirmed progressive disease per PCWG3 on bone scan), or symptoms attributable to prostate cancer. Subsequent management is per physician discretion. The primary endpoint is remaining treatment-free with eugonadal T (> 150 mg/dl) 18 months after the start of treatment interruption, with 75 pts to be enrolled to differentiate 18-month treatment free rates of 0.30 (null hypothesis) and 0.45 (alternative hypothesis). Secondary endpoints include time to eugonadal T, duration off treatment, and changes in patient-reported outcomes. Exploratory endpoints include radiographic progression-free survival, time to next treatment, OS, and correlation of tissue- and blood-based biomarkers with clinical endpoints. The study was activated in July 2022 and accrual is ongoing throughout the NCTN. Support: U10CA180821, U10CA180882, UG1CA189823, https://acknowledgments.alliancefound.org , Veracyte Inc. Clinical trial information: NCT05241860 .

5074 Background: PC commonly expresses PSMA and has dose-responsive radiosensitivity. 177Lu-based radioligands usually use an empiric dosing regimen. This 1st dose-escalation study of 177Lu-PSMA-617 employed a dose-dense fractionation schedule intended to allow delivery of higher total doses to overcome radioresistance due to repopulation. Here, we report mature results of the study. Methods: Progressive mCRPC following > 1 potent ARPI (e.g., abi/enza) and chemo (or unfit/refuse taxane) without limit of # prior therapies provided adequate organ function and ECOG PS 0-2. Treatment: single cycle of fractionated dose 177Lu-PSMA-617 on D1 and D15. In Ph I dose-escalation, patients (pts) received one cycle of 7.4 - 22 GBq followed by Simon 2-stage Ph II at 22.2 GBq. PSMA expression was not required for treatment, but pre- and post-treatment 68Ga-PSMA11 PET/CT and/or 177Lu-PSMA-617 SPECT done. Primary efficacy by PSA changes with 2ndary outcomes with CT/bone scans, PSMA PET, circulating tumor cell (CTC; CellSearch) counts, plasma DNA (PCF_SELECT), and survival. Results: Between 1/2017 – 2/2021, 50 pts treated with median PSA 164.3, 35 (70%) CALGB (Halabi) poor risk. 47 (94%) bone, 38 (76%) nodal, 12 (24%) lung, 5 (10%) liver mets (4 additional pts with PSMA PET+ liver mets not apparent on CT). 29 (58%) with prior >2 ARPI, 29 (58%) with >1 chemo, 14 (28%) with Ra-223, 2 (4%) with 177Lu-J591. 27 (54%) treated at 22 GBq. No dose-limiting toxicity during Ph I. 38 (76%) with any PSA decline, 27 (54%) with >50% PSA. Median rPFS 8.3 mo [5.6-16.7], and OS 15.7 mo [10.9-20.6]. Of 17 RECIST measurable, 6 (35.3%) responded, 7 (41.2%) stable, 4 (23.5%) progressed. Of 31 with paired CTC counts, 16 (52%) decreased, 5 (16%) were stable; 10 (32.3%) converted to favorable/undetectable. Plasma DNA with high allele-specific ploidy and ARcopy number gain associated with OS (univariate). Treatment emergent adverse events (TEAE): 32 (64%) dry mouth, 22 (44%) pain flare, 22 (44%) fatigue, 19 (38%) nausea, 15 (30%) anemia, 15 (28%) thrombocytopenia (plts), 9 (18%) neutropenia (ANC). All TEAEs restricted to grade (Gr) 1-2 except 6 (12%) with Gr 3 anemia, 2 (4%) Gr 3/4 plts, 1 (2%) Gr 3 ANC. TEAE incidence and Gr were not related to dose. On multivariable analysis, 177Lu dose administered (p=0.09), CALGB risk (p=0.04), prior chemo (p=0.009), associated with OS; dose (p=0.1), CALGB risk (p=0.2), and AR copy number (p=0.2) associated with PSA50 decline. Baseline PSMA imaging (by imaging score or SUVmax) was not associated with OS or response. Conclusions: A single-cycle of fractionated-dose 177Lu-PSMA-617 is safe. Despite no pre-selection for PSMA expression, most had PSA decline with favorable PFS and OS compared to historical controls and similar to PSMA-selected targeted radionuclide studies administering multiple cycles in a less dose-intense approach. Clinical trial information: NCT03042468 .

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.

164 Background: Lurbinectedin (L) is a novel inhibitor of oncogenic transcription that was granted accelerated approval by the Food and Drug Administration in June 2020 for the treatment of metastatic small cell lung cancer (SCLC) following disease progression on or after platinum-based chemotherapy (PBC). Prostatic small cell or neuroendocrine carcinoma (SC/NEPC) is a high-grade, invasive malignancy that accounts for < 1% of all prostate cancers. SC/NEPC is distinct from prostatic adenocarcinoma and behaves similar to SCLC. NCCN guidelines for SC/NEPC recommend following the SCLC treatment guidelines. Using these guidelines, L may be used as a second-line treatment in patients (pts) with SC/NEPC who progress on or after PBC. We aimed to characterize the baseline characteristics, clinical course and therapeutic outcomes of pts treated with L for SC/NEPC. Methods: After IRB approval, 18 cases were gathered from 4 academic oncology centers. Baseline patient data, prior treatments and L treatment outcomes, including best radiographic and serologic responses, overall survival (OS), progression-free survival (PFS) and treatment toxicity were assessed. The Kaplan-Meier method was used to calculate OS and PFS from the L start date. Clinical benefit rate (CBR) included pts with complete response (CR), partial response (PR) and stable disease (SD) on imaging. Results: At the time of first L dose, all had metastatic disease with 2-6 distinct sites of metastases, most commonly bone (14/18, 77.8%), lymph nodes (14/18, 77.8%) and liver (13/18, 72.2%); median age was 63.5 (Range: 53-84); 11 pts (61.1%) had an ECOG 0-1; 4 pts (22.2%) had an ECOG of 2-3. The median total number of systemic therapies administered prior to L was 4 (Range: 2-7). All pts received PBC prior to L. The most common dose of L prescribed was 3.2 mg/m2 every 21 days (15/18, 83.3%). Androgen deprivation therapy was administered in conjunction with L in 9 pts (50%). The median number of cycles of L was 5 (Range: 1-10). L was discontinued due to toxicity in 1 patient (5.6%), disease progression in 10 pts (55.6%), transition to hospice in 2 pts (11.1%), 3 pts (16.7%) died while receiving treatment (not due to L toxicity), and 2 pts (11.1%) remained on L at the time of data reporting. The median OS and PFS from date of first L dose was 6.01 months (0.23 – 16.69) and 3.35 months (0.16 – 7.79), respectively. CBR was 9/16 (56.3%) with partial response in 5 pts (31.3%), stable disease in 4 pts (25%), and progressive disease in 7 pts (43.8%). Two pts did not have post-treatment imaging available to assess response. There were no hospitalizations for L treatment related adverse events (tRAE). The most common tRAE were grade I and II fatigue and anemia; 9 pts (50%) experienced no tRAE. The only grade IV toxicity was neutropenia in 3 pts (16.7%). Conclusions: L is a well-tolerated and active treatment option for patients with SC/NEPC. Prospective studies are needed to determine the role of L in the treatment of SC/NEPC.

5021 Background: Somatic mutations in hematopoietic progenitor cells accumulate with age leading to clonal expansion in a process called clonal hematopoiesis (CH). CH increases the risk of developing myeloid neoplasms and shortens overall survival (OS), primarily linked to increased cardiovascular (CV) mortality. The impact of CH in metastatic solid cancers has been conflicting, with shorter OS in a broad cancer cohort but prolonged OS in metastatic colorectal cancer, which may be influenced by prior cytotoxic therapy that can promote emergence of CH. As AR pathway inhibitors (ARPIs) are associated with CV adverse events (AE), exploring the impact of CH in patients (pts) with mCRPC is of interest. Methods: A 9 gene targeted DNA sequencing panel designed to capture common CH mutations ( DNMT3A, TET2, ASXL1, PPM1D, TP53, CHEK2, SRSF2, SF3B1, JAK2) was applied to pre-treatment peripheral blood samples of 957 pts enrolled in the Alliance A031201 phase 3 trial of enzalutamide versus enzalutamide plus abiraterone/prednisone in the first line mCRPC setting. No difference in OS was found between treatment arms. The primary endpoint was the impact of CH on OS; secondary and exploratory endpoints included progression-free survival (PFS) and associations with baseline comorbidities and AEs (hematologic and CV). Cox proportional-hazards and logit models were adjusted for treatment arm, age, and radiation therapy (RT). Results: CH was common with 57% of pts having low CH (VAF>0.5% in 1+ mutation, L-CH), 24% having standard CH (VAF>2%, CH), and 7% having high CH (VAF>10%, H-CH). 4% of pts had 2+ CH mutations and 1% had 3+ mutations. Patients with CH were older (73.1 vs 70.2) and had higher rates of prior RT (58.4% vs 55.7%) and prior chemotherapy (3.9% vs 2.2%). No differences in OS were detected in pts with L-CH, CH, or H-CH. Similarly, no differences in PFS or baseline CV comorbidities were seen in any CH group. Pts with H-CH and TET2-mutated CH had statistically higher odds of any CV event (adjusted p=0.0004 and p=0.010, respectively) There was also a difference in the occurrence of major adverse CV events (MACE) by H-CH status (5.8% vs. 1.9%, adjusted p=0.042), while there was no difference seen for CH (3.4% vs 1.8%, adjusted p=0.147). Regarding hematologic AEs, one pt with a TP53 mutation (VAF 0.94%) developed myelodysplastic syndrome. Conclusions: CH did not affect OS or PFS in pts with mCRPC treated with ARPIs in the A031201 trial. However, CH with VAF>10% and TET2-mutated CH were associated with an increased rate of all CV AEs, suggesting an additive effect of ARPI therapy and CH on adverse CV outcomes. Confirmatory studies are warranted to assess whether CH should be considered in the risk-benefit discussion for pts receiving ARPIs.

PURPOSE Enzalutamide and abiraterone both target androgen receptor signaling but via different mechanisms. The mechanism of action of one drug may counteract the resistance pathways of the other. We sought to determine whether the addition of abiraterone acetate and prednisone (AAP) to enzalutamide prolongs overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) in the first-line setting. PATIENTS AND METHODS Men with untreated mCRPC were randomly assigned (1:1) to receive first-line enzalutamide with or without AAP. The primary end point was OS. Toxicity, prostate-specific antigen declines, pharmacokinetics, and radiographic progression-free survival (rPFS) were also examined. Data were analyzed using an intent-to-treat approach. The Kaplan-Meier estimate and the stratified log-rank statistic were used to compare OS between treatments. RESULTS In total, 1,311 patients were randomly assigned: 657 to enzalutamide and 654 to enzalutamide plus AAP. OS was not statistically different between the two arms (median, 32.7 [95% CI, 30.5 to 35.4] months for enzalutamide v 34.2 [95% CI, 31.4 to 37.3] months for enzalutamide and AAP; hazard ratio [HR], 0.89; one-sided P = .03; boundary nominal significance level = .02). rPFS was longer in the combination arm (median rPFS, 21.3 [95% CI, 19.4 to 22.9] months for enzalutamide v 24.3 [95% CI, 22.3 to 26.7] months for enzalutamide and AAP; HR, 0.86; two-sided P = .02). However, pharmacokinetic clearance of abiraterone was 2.2- to 2.9-fold higher when administered with enzalutamide, compared with clearance values for abiraterone alone. CONCLUSION The addition of AAP to enzalutamide for first-line treatment of mCRPC was not associated with a statistically significant benefit in OS. Drug-drug interactions between the two agents resulting in increased abiraterone clearance may partly account for this result, although these interactions did not prevent the combination regimen from having more nonhematologic toxicity.

e18584 Background: Cancer progression rates following diagnosis are readily measured. However, the progression rate of cancer during the preclinical sojourn time is generally unobserved. Understanding the duration of preclinical stages (“dwell time”) would allow clinicians to better identify appropriate screening intervals for cancer. We therefore elicited estimates of progression rate during the preclinical sojourn time for a wide variety of malignancies from a panel of clinical experts. Methods: We used a validated consensus methodology (RAND/UCLA modified Delphi panel method) to elicit per-stage dwell time estimates for 20 solid cancers and lymphoma from experts. Eleven experienced oncologists (general and subspecialists) from community and academic centers reviewed literature on the natural history of disease and estimated in number of years (<1 to 9+ years) how long it would take each cancer to progress from the beginning of clinically detectable Stage I/II/III to the beginning of the next stage in untreated adults. Cancer histological subtypes were grouped and experts were asked to provide an overall rating. Ratings were completed before and after a discussion of areas of disagreement. Results: Expert estimates and range of dwell time for 21 cancer types are provided in Table. Prostate and thyroid cancer were estimated to be the slowest growing, taking approximately 7 and 5 years respectively to progress through Stage I (range 4-8), 5 years to progress through Stage II (range 3-7), and 3 and 4 (range 2-5) years respectively to progress through Stage III. Esophageal, lung, liver/intrahepatic bile-duct, gallbladder, and pancreatic cancers were estimated to progress quickly through all three stages (1-2 years per stage). Conclusions: These findings summarize practicing oncologists’ estimates of dwell time in preclinical disease. Experts agreed on dwell times although ranges were large and differences in cancer subtypes were not captured. Generally, estimates trend with published data on survival with treatment: cancers with higher survival (e.g., prostate, thyroid) were estimated to grow slower, while cancers with lower survival (e.g., pancreatic, liver/intrahepatic bile-duct, gallbladder) were estimated to grow faster. These estimates could be useful when determining screening intervals for these or any subset of these cancers. [Table: see text]

TPS4593 Background: Bone metastases are prevalent in approximately 30% of pts with advanced RCC. Pts with bone metastases have a worse prognosis compared to pts without bone metastases and are at risk of symptomatic skeletal events (SSEs). Cabozantinib, a multitargeted inhibitor of multiple kinases, including vascular endothelial growth factor (VEGF) receptor and MET, has improved survival in pts with metastatic RCC and has enhanced activity in bone. Ra-223, an alpha-emitting radioisotope with natural bone-seeking proclivity, has been shown to prolong survival in men with castration-resistant prostate cancer. We previously conducted a pilot study of Ra-223 with VEGF inhibition and demonstrated safety and declines in markers of bone formation and resorption with the combination (McKay et al, CCR 2018). Given that decreasing rates of SSEs and improving outcomes for pts with RCC with bone metastases are unmet needs in pts with RCC, we designed a randomized phase 2 study through the National Clinical Trials Network (NCTN) investigating cabozantinib with or without Ra-223 in patients with RCC with bone metastases. Methods: This is an open-label multicenter study. Eligible pts have metastatic RCC of any histology with ≥2 metastatic bone lesions untreated with prior radiation therapy and no more than 2 prior lines of systemic therapy. Pts with non-clear cell RCC are eligible and will be capped at 20% of the total accrual goal. Pts must have a Karnofsky performance status of ≥60%, have symptomatic bone pain defined as a prior SSE or need of analgesics, and be on osteoclast-targeted therapy unless otherwise contraindicated. Pts are randomized 1:1 to cabozantinib with (Arm A) or without (Arm B) Ra-223. Starting dose of cabozantinib for Arm A is 40 mg by mouth daily to be escalated to 60 mg daily after cycle 1 (1 cycle = 28 days) if no persistent grade 2 or grade ≥3 toxicity. Ra-223 is administered at a fixed dose of 1.49 microcurie/kg IV every 28 days x 6 doses. The primary endpoint is SSE-free survival. Secondary endpoints include safety, progression-free survival, overall survival, quality of life measures, and correlative analyses including liquid biopsy studies and tumor tissue analysis. The study has 90% power to detect an improvement in 6-month SSE-free survival rate from 65% to 78% with one-sided α = 0.025 significance. To ensure 191 evaluable patients, target accrual is 210 pts. This design includes a safety run-in and an interim analysis for futility when 50% of the expected number of events (72 SSE events) have been observed. Final data analysis will occur when 143 events have been observed. The study was activated in December 2019 and accrual is currently ongoing throughout the NCTN. Clinical trial information: NCT04071223.