Chaudhuri, Aadel A.

TPS898 Background: Enfortumab vedotin with pembrolizumab (EV/Pembro) is now first-line therapy for locally advanced or metastatic urothelial carcinoma (la/mUC) following the EV-302/KEYNOTE-A39 trial, which demonstrated a 67.7% response rate and prolonged survival. However, ~35% of cancers exhibited primary resistance and most responders relapse within one year, with post-EV/Pembro therapies achieving < 15% response and median survival < 3 years. We previously showed that therapeutic plasma exchange (TPE) removed soluble PD-L1 and other immune checkpoint inhibitor (ICI) blocking soluble factors from the blood and that this overcame ICI resistance. Combining TPE with EV/Pembro rechallenge may overcome acquired resistance and restore antitumor immunity. Methods: RECIPE-B1 [NCT07087860] is an open-label, randomized phase II trial enrolling 50 patients (1:1) with EV/Pembro-refractory la/mUC and ECOG 0–2. Arm A receives TPE on days 1–3 followed by EV 1.25 mg/kg IV plus pembrolizumab 200 mg IV on day 3 of each 21-day cycle for the first three cycles, then continues EV/Pembro alone from cycle 4. Arm B receives investigator’s-choice next-line standard of care (SOC) per NCCN guidelines. Tumor assessments occur at the end of cycle 4 (±28 days) and every 12 weeks thereafter; safety is monitored each cycle (CTCAE v5.0). The primary endpoint is objective response rate (ORR) by RECIST 1.1, comparing TPE + EV/pembro versus SOC. Secondary endpoints include progression-free survival, overall survival, duration of response, quality of life (EORTC QLQ-CIPN20), and safety. Correlative studies evaluate circulating and urinary tumor DNA and exosomal biomarkers (including exosomal Nectin-4) as predictors of response and resistance. The trial is open at Mayo Clinic; as of September 2025, 2 of 50 patients have been enrolled, with planned accrual of ~2 patients/month and central coordination at Mayo Clinic and affiliates. Clinical trial information: NCT07087860 .

TPS283 Background: Emerging evidence suggests that metastasis-directed therapy (MDT) with stereotactic body radiotherapy (SBRT) can delay systemic therapy in oligometastatic castration-sensitive prostate cancer (omCSPC). However, the optimal timing of androgen deprivation therapy (ADT) and androgen receptor pathway inhibitor (ARPI) initiation in this setting remains undefined. While deferred ADT following MDT may preserve quality of life, early short-course ADT/ARPI may eradicate micrometastatic disease and extend progression-free survival. Extracellular vesicles (EVs) carrying PSMA-positive prostate cancer (PC) signals and circulating tumor DNA (ctDNA) may serve as real-time biomarkers of MRD and treatment response. Methods: DIVINE [NCT06378866] is an open-label, phase II, randomized trial enrolling men with omCSPC defined by 1–5 metastases (≥1 extrapelvic) on conventional imaging (CT/MRI and bone scan) and testosterone >100 ng/dL. PSMA PET may be obtained for correlative purposes but does not determine eligibility. Participants (N = 220) are randomized 1:1 to: Arm A (Early systemic): SBRT plus 6 months of ADT + ARPI. Arm B (Deferred systemic): SBRT alone with observation, reserving systemic therapy until radiographic progression not amenable to further SBRT (mrPD). SBRT is delivered per institutional standard; repeat SBRT is allowed until lesions become non-addressable. The primary endpoint, modified radiographic progression-free survival (mrPFS), is the time from randomization to death or radiographic progression not amenable to further MDT, defined by PCWG3 (bone) and modified RECIST 1.1 (soft tissue) criteria on conventional imaging. Soft-tissue progression requires ≥ 20% increase in measurable disease or a new lesion; bone progression requires ≥ 2 new confirmed lesions. Secondary endpoints include OS, biochemical PFS, time to local and distant progression, and grade 3–5 adverse events during systemic therapy. Exploratory endpoints evaluate EV and ctDNA kinetics as MRD markers, correlation of PSMA-positive EV burden with outcomes, and duration of response after short-course ADT/ARPI. Correlative analyses will longitudinally quantify PSMA-positive EVs and ctDNA at baseline, on treatment, and at progression to define MRD dynamics and resistance patterns. The trial uses Pocock–Simon dynamic allocation by EV strata and metastatic burden to ensure balance across arms. The trial is open and actively enrolling across all Mayo Clinic sites; as of October 2025, 35 of the planned 220 patients have been accrued. Clinical trial information: NCT06378866 .

214 Background: 177 Lu-PSMA-617 (LuPSMA) has revolutionized care for patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC), but only half achieves PSA decline ≥50%. Biomarkers are urgently needed to improve pt selection. EVs and ctDNA released by cancer cells into the blood are emerging biomarkers to estimate overall tumor burden and capture tumor heterogeneity in mCRPC. Here, we analyzed pre-treatment plasma levels of tumor EVs and ctDNA in a pilot cohort of 35 pts with mCRPC treated with LuPSMA. Methods: Blood samples were collected pre-cycle 1 of LuPSMA at Tulane Cancer Center between 12/2018-1/2025. Plasma-derived small and large EVs were incubated with fluorescently conjugated antibodies and enumerated using nanoscale flow cytometry. ctDNA fraction was estimated from plasma cfDNA methylation WGS (∼10×) with ichorCNA. We also analyzed EVs from blood samples of male healthy donors (HD) and pts with localized prostate cancer (LPC) collected 1 day to 8 months after radical prostatectomy (post-RP) from 6/2020-8/2024 at Mayo Clinic as controls. Results: Median age at collection for 10 HD was 55 yrs and for 36 pts with LPC post-RP was 65 yrs. Median PSMA+ EV level was 2.0 x 10 6 /mL for post-RP and 1.4 x 10 6 /mL for HD. For 35 pts with mCRPC, 25 pts had complete data for analysis. Median PSMA+ EV level was 1.4 x 10 7 /mL, significantly higher than post-RP (p<0.001) and HD (p<0.001). At LuPSMA start, median age was 69 yrs (range 54-83), PSA was 82 ng/mL (range 0.8-503), median time from CRPC diagnosis to start was 50 months (range 6.9-285), median time from plasma collection to treatment initiation was 0.5 months (range 0-7.3). Median number of prior lines of life-extending therapy was 4 (range 1-11), including 100% androgen receptor pathway inhibitor and 75% docetaxel. Pts received median 4 cycles of LuPSMA. Median ctDNA fraction was 14.0% (range 0-51.1). Median time to reach nadir PSA for pts with any decline was 2.6 months. 15 pts (60%) achieved PSA40 (defined ≥40% decline in PSA from start to nadir) (range -99% to -42%) compared to 10 pts (40%) who did not (range -16% to rise), which predicted better median overall survival (OS) after LuPSMA start (40.7 v 6.0 months; HR 0.23, 95% CI, 0.07-0.71; p=0.0001). Pts were classified as LuPSMA responders using PSA40. Responders had a lower ratio of large to small PSMA+ EVs (0.30 v 0.53, p=0.0042) with an area under the receiver operating characteristic curve (AUC) of 0.83 (95% CI, 0.68-0.99), and a lower median ctDNA fraction (6.1% v 26.2%, p=0.0044) with an AUC of 0.83 (95% CI, 0.68-1.00). Incorporating both PSMA+ EV and ctDNA fraction together predicted PSA40 response with an AUC of 0.93 (95% CI, 0.84-1.00, p=0.0003). Conclusions: Using pre-LuPSMA plasma samples from a heavily pre-treated historical cohort, we integrated non-invasive liquid biopsy methods to successfully predict response to LuPSMA using PSA decline. Prospective validation is underway.