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Abstract BACKGROUND [177Lu]Lu-PSMA-617 improves survival and quality of life in men with metastatic castration-resistant prostate cancer but requires substantial healthcare involvement. Our analysis evaluated the time toxicity associated with [177Lu]Lu-PSMA-617, representing the first dedicated radioligand time toxicity assessment. MATERIALS AND METHODS We conducted a multi-institutional retrospective study of patients initiating [177Lu]Lu-PSMA-617 between April 2022 and March 2023. Patients were followed from first [177Lu]Lu-PSMA-617 administration until 3 months after the final cycle, initiation of new systemic therapy, or death. Time toxicity was quantified as healthcare contact days during the at-risk interval. Associations with baseline characteristics were evaluated using negative binomial regression models. Univariate and multivariable models were performed. RESULTS Among 135 patients, median age was 69 years and median prior systemic therapies was 4. Patients completed a median of 5 [177Lu]Lu-PSMA-617 cycles over 7.6 months. Median healthcare contact days were 20 (IQR, 15–28), representing 9.5% (IQR, 6.4–13.9) of at-risk days. Fifteen patients (11%) experienced high time toxicity (>1 contact day per 5 days), while 42 (31%) had low time toxicity (≤1 contact day per 14 days). Among the 57 patients who received both cycle 1 and cycle 6, mean per cycle healthcare contact days were 4 and 3.6, respectively (paired Wilcoxon signed-rank test, p = 0.04). Routine oncology visits comprised 32.7% of contact days, compared with 8.8% from hospitalizations. Lower baseline hemoglobin was independently associated with greater time toxicity (RR = 0.87; 95% CI, 0.79–0.96; p = 0.004). CONCLUSION In heavily pretreated patients, [177Lu]Lu-PSMA-617 demonstrated relatively low time toxicity, supporting it as a time-efficient therapy.

Abstract Introduction: Next generation of Theranostics studies are looking at novel combinations with radiation sensitizers to enhance PRRT’s efficacy. Here, we present safety and efficacy data from a multi-center phase 1 study of a [¹⁷⁷Lu]lutetium-dotatate -triapine combination in patients with GEP-NETs. Methods: The study consisted of two phases (dose escalation and expansion) administering the recommended phase 2 doses (RP2D) for the two agents. All patients received 200 mCi of [¹⁷⁷Lu]lutetium-dotatate on day 1 of four 8-week cycles, in combination with oral triapine administered at assigned dose levels (100 mg, 150 mg or 200mg) from days 1 to 14 of each cycle. Results: A total of 31 (A: 15 ; B: 16 ) patients received treatment. Nine patients experienced dose-limiting toxicities; Grade 3 anemia (n=1), Grade 5 cardiac arrest (n=1), and Grade 4 neutropenia (n=7). Based on the overall safety and pharmacokinetics data, a [¹⁷⁷Lu]lutetium-dotatate (200 mCi) plus triapine (150 mg) dose was selected as the RP2D for the expansion phase. Grade ≥3 treatment related adverse events were observed in 77% patients: anemia (23%), nausea and vomiting (3% ), lymphopenia ( 58%), neutropenia ( 35%) and leukopenia ( 39%). The majority of cytopenias were transient and resolved within two weeks. Among the 28 evaluable patients, the objective response rate (ORR) was 21.4% and the median progression-free survival (mPFS) has not been reached (median follow-up period: 23.7 months). Conclusions: The combination of [¹⁷⁷Lu]lutetium-dotatate (200 mCi) and oral triapine (150 mg D1-14) was well tolerated and demonstrated preliminary activity in patients with well-differentiated GEP-NETs. (NCT04234568).

PURPOSE Bone metastases (BM) occur in approximately 30% of patients with metastatic renal cell carcinoma (mRCC) and are associated with poor survival and symptomatic skeletal events (SSEs). Radium-223, an alpha-emitting bone-seeking radioisotope, and cabozantinib, a tyrosine kinase inhibitor, have demonstrated activity in BM. RADICAL (Alliance A031801; ClinicalTrials.gov identifier: NCT04071223 ) evaluated cabozantinib ± radium-223 in mRCC with BM. METHODS This phase II trial enrolled patients with mRCC of any histology with ≥1 BM. Patients were randomly assigned 1:1 to cabozantinib ± radium-223, stratified by osteoclast-targeted therapy (OTT), prior therapy, opioid use, and International mRCC Database Consortium (IMDC) risk. The primary end point was SSE-free survival (SSE-FS). Secondary end points included safety, objective response rate (ORR), progression-free survival, and overall survival (OS). A target of 124 evaluable patients was planned, with a prespecified interim futility analysis at 50% of expected SSE-FS events; the trial would stop if the stratified hazard ratio (sHR) > 1.0. RESULTS The prespecified interim futility analysis was conducted after 90 patients were enrolled and crossed the futility boundary, leading to closure at 98 patients. The final analysis included all 98 patients. Median age was 63 years, 82.7% had clear cell histology, and 79.6% were using an OTT. IMDC risk was favorable (18.4%), intermediate (67.3%), and poor (14.3%). Median follow-up was 13.1 months. Median SSE-FS for cabozantinib with radium-223 versus cabozantinib was 16.7 versus 17.6 months (sHR, 1.46 [90% CI, 0.86 to 2.51]). Median OS was 28.3 versus 19.7 months (sHR, 1.40 [95% CI, 0.70 to 2.79]). ORR was 19.4% versus 25.0% ( P = .78). Grade ≥3 adverse events were similar across arms (69.6% v 75.5%). CONCLUSION Radium-223 did not improve SSE-FS when added to cabozantinib. The combination demonstrated a manageable safety profile.

4500 Background: BM occur in ~30% of RCC pts and are associated with poor survival and symptomatic skeletal events (SSEs). Radium-223, an alpha-emitting bone-seeking radioisotope, prolongs survival in advanced prostate cancer. A pilot study of radium-223 with VEGF tyrosine kinase inhibitors (TKI) in RCC with BM showed safety and early efficacy (McKay, CCR, 2018). Cabozantinib is a TKI that showed efficacy in BM. RADICAL (NCT04071223) was designed to investigate cabozantinib ± radium-223 in RCC with BM. Methods: This open label multicenter study enrolled RCC pts with ≥1 symptomatic BM not previously irradiated and Karnofsky performance status ≥60%. Prior therapies were allowed; non-clear cell population was limited to 20%. Randomization was 1:1 to cabozantinib with (Arm A) or without (Arm B) radium-223, stratified by osteoclast-targeted therapy (OTT), prior therapy, baseline opioid use, and IMDC risk. In Arm A, cabozantinib was 40 mg daily cycle 1, 60 mg thereafter if tolerated; radium-223 was 1.49 microcurie/kg IV every 28 days for 6 doses. In Arm B, cabozantinib was 60 mg daily. The primary endpoint was SSE-free survival (SSE-FS). Secondary endpoints were safety, objective response rate (ORR), progression-free survival (PFS) and overall survival (OS). The study was designed with 85% power to detect improvement in 6-month SSE-FS from 65% to 78% (one-sided α=0.05), with planned interim futility analysis at 50% of expected events. Results: From 12/2019 to 9/2025, 90 pts were enrolled and evaluable for the interim analysis. Median age was 63 years; 74.4% male, 90.0% White, 83.3% clear cell histology. 11.1% were treatment naïve, 80.0% received OTT, 51.1% had baseline opioid use. IMDC risk was 16.7% favorable, 68.9% intermediate, 14.4% poor. Median cabozantinib dose was 31.4 mg (Arm A) and 40.0 mg (Arm B); median radium-223 cycles was 6. Median follow-up was 13.1 (range 0.1-49.4) months with 50 events, 17 SSEs (Arm A: 10; Arm B: 7) and 33 deaths (Arm A: 13; Arm B: 20). Outcomes are in Table. 71 pts were evaluable for response. ORR was 22.2% (Arm A), 22.9% (Arm B). Any grade treatment-related adverse events were 97.7% (Arm A), 93.2% (Arm B); grade ≥3 were 65.9% (Arm A), 56.8% (Arm B). The trial closed after interim analysis as SSE-FS did not meet the prespecified futility boundary (HR≤1). Conclusions: Radium-223 did not improve the primary endpoint of SSE-FS when added to cabozantinib but a numerical prolongation in OS was observed. Combination treatment was safe. Alternative radiotherapeutics warrant investigation in RCC. Clinical trial information: NCT04071223 . Interim efficacy analysis. Arm Median(95% CI) HR (95% CI) Stratified SSE-FS A 17.9 (15.0-NE) 1.24 (0.62-2.48) B 17.6 (10.9-NE) Unstratified SSE-FS A 17.9 (15.0-NE) 0.90 (0.51-1.59) B 17.6 (10.9-NE) OS A 32.2 (17.9-NE) 0.77 (0.42-1.41) B 21.3 (12.3-NE) Stratified PFS A 11.0 (5.8-17.4) 1.39 (0.72-2.66) B 11.2 (9.0-18.5)

PURPOSE 177Lu-PSMA-617 (LuPSMA) is an approved prostate-specific membrane antigen (PSMA)–targeted radiopharmaceutical therapy for men with metastatic castration-resistant prostate cancer (mCRPC). Older patients, particularly octogenarians, represent a substantial proportion of men with mCRPC but have been traditionally underrepresented in key registrational trials of LuPSMA. METHODS This retrospective multi-institutional study evaluated patients age 80 years and older with mCRPC after chemotherapy treated with ≥1 cycle of LuPSMA from August 2022 to December 2024. Clinical and demographic data were abstracted from electronic medical records. Outcomes included prostate specific antigen (PSA) response (PSA50 and PSA90), progression-free survival (PFS), overall survival (OS), and toxicities. Kaplan-Meier methods estimated PFS/OS; descriptive statistics summarized baseline and safety data. RESULTS Ninety-five patients (median age, 83 years) were included, of whom 36 (38%) and 21 (22%) had a history of cardiac disease or chronic kidney disease, respectively. Median follow-up was 24.1 months (IQR, 6.7-28.1). Patients received a median of five cycles of LuPSMA. Fifty-two (57%) and 21 (23%) patients achieved a PSA50 and PSA90, respectively. Median PFS and OS were 7.3 months (95% CI, 6.4 to 8.7) and 13.5 months (95% CI, 9.7 to 18.8), respectively. Grade ≥3 hematologic toxicities included anemia (n = 19; 20%) and thrombocytopenia (n = 4, 4%); grade ≥3 acute kidney injury occurred in one patient. Fourteen (15%) patients had dose delays, seven (7%) required reductions, and 10 (11%) discontinued therapy due to toxicity. Thirty-seven patients (39%) were hospitalized during therapy, with intensive care unit-level care required in two patients (2%), and there was one treatment-related death. CONCLUSION LuPSMA had comparable outcomes in octogenarians with mCRPC to patients on registrational trials, although 2/5 of patients required hospitalization during therapy. These findings support the feasibility and efficacy of LuPSMA in well-selected older men with mCRPC and suggest a role for closer monitoring of older patients.

TPS290 Background: Landmark randomized trials established the survival benefit of adding D to ADT in mCSPC. Building on this foundation, subsequent trials (PEACE-1 and ARASENS) demonstrated further survival improvements when androgen receptor pathway inhibitors (ARPI) were added to the ADT + D backbone. However, the independent contribution of D within the triplet regimen remains unclear given lack of prospective evaluation. Additionally, tumor suppressor gene (TSG) alterations involving TP53, PTEN, and RB1 are frequently observed in PC and are associated with aggressive biology and poor outcomes, providing an opportunity to enhance prognostic accuracy and optimize selection of candidates for treatment intensification. We hypothesize that adding D to ADT plus A will improve survival compared to ADT + A in mCSPC and stratification by TSG status may identify different treatment effects across molecular subgroups. Methods: ASPIRE is an open-label, two-arm, randomized phase 3 study to assess the benefit of D added to ADT plus A for patients with mCSPC. Eligible patients include those with confirmed adenocarcinoma of the prostate with evidence of distant metastatic disease on conventional imaging and are appropriate to receive D. Patients with metachronous low-volume disease or PSMA-PET only disease are excluded. Candidates must have next-generation sequencing (NGS) results from a CLIA-certified tissue test available for TSG status stratification at registration. Eligible patients will receive ADT plus A (240 mg PO daily) +/- D for up to 6 cycles until progression of disease by PCWG3/RECIST version 1.1 criteria. Prior therapy with ADT (with or without ARPI) initiated within 120 days before registration is permitted. The primary endpoint is overall survival (OS). Secondary endpoints include OS by TSG status; radiographic progression-free survival (rPFS); time to castration resistance; symptomatic skeletal event–free survival; time to worsening of disease-related symptoms (NCCN-FACT FPSI-17); safety and tolerability (CTCAE v5.0); PSA90 response at 6 weeks and 6 months; time to PSA progression; and objective response rate in patients with measurable disease. The study will enroll 1200 patients and is currently actively accruing patients. Clinical trial information: NCT06931340 .

Black patients with metastatic prostate cancer have higher mortality rates compared to non-Hispanic White patients. There are no data on outcomes with [177Lu]Lu-PSMA-617 (LuPSMA) across racial groups. We evaluated the association between race and outcomes with LuPSMA in a multi-institutional cohort of consecutive patients with mCRPC treated with LuPSMA. The primary outcomes were PSA-50 rate, PSA-progression-free survival (PSA-PFS), and overall survival (OS). Statistical models were adjusted for age, number of prior therapies, sites of metastases, and baseline PSA. A total of 654 patients were included; 593 (91%) were White, 45 (7%) were Black and 16 (2%) were another non-Black minority (NBM). There were no statistically significant differences in PSA-50 rates, PSA-PFS and OS between the groups. Black and White patients treated with LuPSMA had similar clinical outcomes; efforts are needed to ensure Black and NBM patients have equal access to life prolonging therapies to narrow disparities in outcomes.

TPS11579 Background: Gastrointestinal stromal tumors (GIST) are commonly driven by mutations in the receptor tyrosine kinase KIT . Resistance to approved tyrosine kinase inhibitors (TKIs) arises from additional KIT mutations in the ATP-binding pocket (AP) and activation loop (AL). No single approved TKI broadly suppresses all resistant clones, and overlapping VEGFR inhibition and toxicity limits TKI combinations. The type I TKI bezuclastinib (“BEZ,” CGT9486) inhibits KIT AL resistance mutations, does not inhibit VEGFR, and has complimentary activity with sunitinib (“SUN,” inhibitor of KIT AP resistance mutations). The first-in-human study (PLX121-01) and ongoing Peak trial (NCT05208047) evaluated BEZ+SUN showing promising safety and efficacy in GIST. SARC044 investigates BEZ+SUN in patients (pts) with SUN-resistant, KIT-mutant GIST, and correlatives aim to determine mechanisms of response and resistance (NCT06208748). Methods: SARC044 is a multi-center, open label, single-arm phase II trial enrolling up to 40 adult pts with KIT exon 9 or 11-mutant GIST resistant to imatinib and SUN. After TKI washout (baseline, “b/l”), pts initiate BEZ 600 mg daily for 2 weeks, then add SUN 37.5 mg daily, taking both drugs continuously (28-day cycles) until mRECISTv1.1 progression or unmanageable toxicity. Response evaluations (RE) are performed every 8 weeks (wk) through 15 months (mo) on study, then every 12 wk. Circulating tumor DNA (ctDNA) is collected at b/l, cycle 1 day 15 (C1D15), C2D1, C3D1, and progression. Targeted exome sequencing (TES) of ctDNA will track primary/resistant KIT mutation dynamics across therapy. 18 FDG PET/CTs are performed in 20 pts at b/l, C1D15, and C2D1, which guide a biopsy of a resistant tumor. TES, allele-specific and long-read PCR (to detect AP+AL mutation phasing), and immunoblotting (evaluating KIT pathway activation) will be performed on tissue. EORTC QLQ-C30 surveys collect pt-reported outcomes (PRO) at b/l, on treatment, and at progression. The primary endpoint is median progression-free survival (mPFS) and secondary endpoints include overall survival at 1 and 2 years, clinical benefit rate at 16 wk, adverse event rate, PRO, and KIT mutation profile in ctDNA and tissue. 35 evaluable pts achieves 83% power (p<0.05, one-sided) in a one-sample log-rank test to detect a mPFS of 6.5 mo vs 4 mo (historic control). Expected accrual is 12 mo across 4 sites in the United States with ~36 mo to study completion. Clinical trial information: NCT06208748 .

TPS4616 Background: Osseous metastases (OM) occur in approximately 30% patients with advanced RCC. Despite therapeutic advances, OM are associated with poor survival and risk of symptomatic skeletal events (SSEs). Cabozantinib targets multiple tyrosine kinases, including vascular endothelial growth factor (VEGF) receptors and MET (Mesenchymal-Epithelial Transition factor), which are overexpressed in OM, contributing to cabozantinib’s enhanced bone activity. Radium-223, an alpha-emitting bone-seeking radioisotope, prolongs survival in men with metastatic castration-resistant prostate cancer to the bone. Building on this therapeutic approach targeting OM, our pilot study of radium-223 with VEGF inhibition in RCC with OM has also shown safety, improvement in circulating bone turnover markers, and early efficacy (McKay et al, CCR 2018). To address the unmet need to improve SSE rates and outcomes in RCC and OM, we designed a study investigating cabozantinib with or without radium-223 in patients with RCC with OM (NCT04071223). Methods: This is an open-label, multicenter randomized phase-2 study. Key inclusion criteria include metastatic RCC of any histology with ≥1 OM, at least 1 OM without prior radiation, any number of prior therapies, and Karnofsky performance status ≥ 60%. Use of a bone protecting agent is required unless contraindicated. Patients are randomized 1:1 to cabozantinib with (Arm A) or without (Arm B) radium-223. The 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. Radium-223 is administered at a fixed dose of 1.49 microcurie/kg IV every 28 days x 6 doses. The starting dose for cabozantinib in Arm B is 60 mg daily. The primary endpoint is SSE-free survival. Secondary endpoints include safety, progression-free survival, overall survival, time to first SSE, objective response rate, time to subsequent anti-cancer therapies, quality of life (QoL) measures, and correlative analyses including liquid biopsy and tumor tissue analysis. The study is designed to have 85% power to detect an improvement in 6-month SSE-free survival rate from 65% to 78% with one-sided α = 0.05 significance. To ensure 124 evaluable patients, target accrual is 134 (67 per arm). The group-sequential design includes a safety run-in and an interim analysis for futility when 50% of the expected number of events have been observed. The safety run-in, performed in the first 12 patients randomized to combination therapy, did not demonstrate dose limiting toxicities. Final data analysis will occur when 99 events have been observed. The study was activated in July 2020 and accrual is ongoing throughout the National Clinical Trials Network (NCTN). Continued site participation and enrollment are essential to evaluate this therapeutic strategy. Clinical trial information: NCT04071223 .