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Aim: Despite advances with immune checkpoint inhibitor (ICI)-based regimens in the past decade, patients with metastatic urothelial cancer (mUC) face a poor prognosis with few approved options. Platinum-based chemotherapy with paclitaxel and carboplatin (TC) +/– ICI may be a feasible choice. Methods: We generated an IRB-approved, HIPAA-compliant retrospective database of patients at Mayo Clinic Cancer Center with mUC who started TC +/– ICI after disease progression on ICI from January 2018 through December 2024. Baseline demographics, clinicopathologic features, and treatment outcomes were extracted from the electronic health record. Kaplan-Meier method was used to calculate median duration of response (DOR), progression-free survival (PFS) and overall survival (OS). Results: There were 32 patients who fit inclusion criteria, including 31 patients who had disease progression on ICI in the metastatic setting and 1 patient who developed metastatic disease on adjuvant nivolumab. Patients received a median of 4 cycles (range 1–14) of TC over median 12 weeks (range 3–53). Overall, 81% of patients received TC concurrently with an ICI, and 28% continued maintenance ICI after TC discontinuation (at the treating oncologist’s discretion due to adequate response or toxicity). The best objective response rate was 41% and disease control rate was 75%, with median DOR of 4.8 months (IQR 2.7–10.4), median PFS of 4.6 months (IQR 3.3–10.2), and median OS of 9.4 months (IQR 6.3–15.9). Some patients in this series had very durable responses with PFS > 12 months and OS > 24 months. TC +/– ICI was overall well tolerated with expected type and severity of adverse events. Conclusions: Strategies to overcome ICI resistance are needed, and TC +/– ICI after disease progression on an ICI shows promising tolerability and efficacy in this setting for patients with mUC. Our series was notable for some patients having a durable response. Validation in larger cohorts is warranted.

Background/Objectives: Tumor-infiltrating lymphocyte (TIL) therapy is an important option for patients with metastatic melanoma progressing after standard systemic therapy, but real-world data on treatment delivery, toxicity monitoring, and immune recovery remain limited. We evaluated clinical outcomes, treatment tolerance, immune reconstitution, and cardiac biomarker dynamics across three Mayo Clinic sites. Methods: We retrospectively analyzed adults with metastatic melanoma who received lymphodepleting chemotherapy followed by TIL infusion and high-dose interleukin-2 (IL-2) between April 2024 and December 2025. Clinical outcomes, treatment delivery, and adverse events were assessed. Longitudinal immune monitoring included CD4 and CD8 T-cell counts, CD4:CD8 ratio, and immunoglobulin G (IgG) at baseline and follow-up. In a prespecified cardiac sub-cohort, high-sensitivity troponin (hs-Tn) was measured during IL-2 administration to evaluate associations with cardiac events and IL-2 interruption. Results: Thirty-six patients underwent TIL infusion. The objective response rate was 50.0%, including complete responses in 13.9%, and the disease control rate was 72.2%. Median progression-free survival was 3.61 months, and median overall survival was 12.94 months. M1d disease was associated with inferior overall survival on univariable analysis (HR 6.55, 95% CI 2.03–21.17; p = 0.002), with attenuation after multivariable adjustment. Receipt of ≥3 IL-2 doses was associated with longer overall survival on univariable analysis (HR 0.20, 95% CI 0.06–0.64; p = 0.007), but this association also attenuated after adjustment. Longitudinal immune monitoring demonstrated persistent CD4 lymphopenia through 6 months, sustained inversion of the CD4:CD8 ratio, and declining IgG at months 3 and 6. In the cardiac sub-cohort (24 patients; 87 IL-2 doses), post-dose hs-Tn ≥15 ng/L was associated with clinically significant cardiac events (OR 9.6, 95% CI 1.5–60.6; p = 0.016) and IL-2 interruption (OR 3.4, 95% CI 1.1–10.7; p = 0.036). For cardiac events, hs-Tn ≥15 ng/L had 100% sensitivity and 100% negative predictive value. Conclusions: In routine practice, TIL therapy was feasible and active in metastatic melanoma. M1d disease identified a subgroup with poor survival, peri-dose hs-Tn showed promise as a tool to support safer IL-2 delivery, and prolonged CD4 suppression with IgG decline suggests that recovery after TIL therapy extends beyond initial hematologic reconstitution. These findings support prospective validation of biomarker-guided IL-2 monitoring and extended post-treatment immune surveillance.

e23276 Background: More than 50,000 patients with cancers of all stages were enrolled in the E2C2 trial, which captured patient-reported data across 6 symptom domains (SPPADE): sleep, pain, impaired physical function, anxiety, depression, and energy deficit or fatigue. This trial offers a unique opportunity to evaluate the evolution of symptom burden as prostate cancer (PCa) advances and the association of symptom burden with prognosis in the various disease states. Methods: The cohort was derived by cross-referencing participants in the E2C2 study with the Mayo Clinic Cancer Registry for more granular data on disease state and treatment characteristics, focusing on PCa. Symptoms were patient-reported on a 0-10 numerical rating scale, categorized as none/mild (0-3), moderate (4-6), and severe (7-10). We compared the prevalence of symptom burden across disease states, using the first survey completed by patients, in 3 groups: (1) non-metastatic (localized, locally advanced, and biochemically recurrent), (2) metastatic hormone sensitive (mHSPC), and (3) castration resistant (CRPC), using chi square tests. We then used log-rank tests to compare survival distributions based on symptom severity within each disease state. Results: A total of 1,011 patients were included. The distribution of moderate to severe symptoms by disease state is shown in Table 1. Fatigue, impaired physical function, and pain were more prevalent in patients with advanced disease, whereas the prevalence of depression and anxiety was not statistically different by disease state. Greater fatigue and physical impairment were consistently associated with poorer OS across all disease states, including patients with non-metastatic disease (p < 0.001). Pain was most strongly associated with inferior outcomes in the more advanced disease states of mHSPC (p < 0.001) and CRPC (p < 0.001). Anxiety (p < 0.001) and depression (p = 0.001) were only prognostic in CRPC patients. Conclusions: SPPADE symptoms are common in PCa. Physical symptoms are greater in more advanced disease, yet the high burden of unmet psychologic needs is similar across the disease states. Notably, severe patient-reported fatigue and physical dysfunction are strongly prognostic even in early disease, suggesting they are markers of physiologic vulnerability. Structured symptom monitoring may improve the identification of high-risk patients. Clinical trial information: NCT03892967 . Moderate to severe symptoms by disease state. Non-Metastatic (N= 243) mHSPC (N= 479) CRPC (N= 289) P-value Pain, n (%) 51 (21.3) 121 (25.5) 100 (35.1) 0.001 Fatigue, n (%) 92 (38.3) 230 (48.6) 163 (57.2) <0.001 Impaired Physical Function, n (%) 79 (32.5) 180 (37.7) 146 (50.7) <0.001 Sleep Disturbance, n (%) 72 (30.1) 167 (35.2) 104 (36.1) 0.3 Depression, n (%) 47 (19.6) 92 (19.4) 63 (22.0) 0.67 Anxiety, n (%) 56 (23.4) 93 (19.6) 68 (23.9) 0.3

e13730 Background: Financial toxicity, the burden of treatment cost, affects up to half of people with cancer and can affect survival. Financial toxicity is a health equity issue, disproportionately affecting Black patients. This cross-sectional study used baseline data from the Discussions of Cost (DISCO) Trial, an RCT to improve patient-provider treatment cost discussions and, in turn, mitigate financial toxicity, to examine whether Black and White patients differed in patient-provider communication perceptions and financial toxicity correlates. Methods: Data were collected from 2021-2025 at an NCI-designated comprehensive cancer center. Participants were Black or White patients diagnosed with solid tumor cancers. At baseline, patients completed demographic measures; communication measures of self-efficacy in patient-provider interactions (e.g., “I am confident I know what questions to ask a provider”); self-efficacy in managing cancer treatment costs (e.g., “I am confident I can understand treatment costs”); and whether they have a provider- or patient-centered approach (e.g., “the provider should decide what gets talked about”); and financial measures including economic burden (e.g., “it’s difficult to live on my income”); treatment cost distress (e.g., “worries about paying for my cancer treatment keep me up at night”); and anticipated material hardship (e.g., “I worry about the financial problems I will have in the future as a result of my treatment”). Comparisons were conducted by patient race. Results: A total of 202 patients participated (116 Black patients, 86 White patients). White patients were more likely to have advanced degrees, a higher annual income, and less likely to have Medicaid compared to Black patients. Black patients reported higher self-efficacy for managing treatment costs ( p = .002) and a higher provider-focused orientation to the patient-provider relationship ( p = .001), than White patients. Black patients reported greater levels of financial burden ( p < .001), cost distress ( p = .005), and anticipated material hardship ( p = .003). There was no difference in self-efficacy for interacting with providers. Conclusions: These results suggest that a communication intervention for patients may help mitigate the experience of financial toxicity, especially for Black patients. Clinical trial information: NCT04766190 . Patient characteristics. Black Patients White Patients p -value Race 116 86 Education < High School High School/GED Some College 2 or 4-year College Degree Graduate/Professional College Trade/Technical/Vocational School 10352626712 0141631187 < .001 Annual Household Income 0 - $19,999 $20,000 - 39,999 $40,000 - 59,999 $60,000 - 79,999 $80,000 - 99,999 $100,000 - 149,999 $150,000 + 53201611431 51215991716 <.001 Insurance Type* Medicaid Medicare Medicare supplement Private None 604911330 113726393 <.001>.99<.001.20.15 *Patients could select more than one

e13729 Background: Financial toxicity, the burden of treatment cost, affects up to half of people with cancer and can affect survival. Financial toxicity is a health equity issue, disproportionately affecting Black patients. Patient education about cost and patient-provider cost discussions are recommended to mitigate financial toxicity but occur infrequently. The Discussions of Cost (DISCO) App, designed to mitigate financial toxicity through a tailorable education and communication intervention, was assessed for efficacy in an RCT with Black and White patients. Here we describe the DISCO App's feasibility and acceptability. Methods: Data were collected from 2021 to 2025 at an NCI-designated comprehensive cancer center. Participants were Black or White patients diagnosed with solid tumor cancers. While waiting to see their provider, patients randomized to the intervention arm used the DISCO App on a tablet. The DISCO App includes a video about treatment costs, ways to manage costs, and the importance of discussing costs with providers. Once patients enter their socio-demographic information (e.g., employment) and financial concerns, they receive a tailored list of cost questions to ask their provider. Patients responded to measures immediately after using the DISCO App. Feasibility was assessed by patient reports of how much time they needed to use the DISCO App and if they were able to use the DISCO App before the provider entered the exam room. Acceptability was measured by items assessing patient perceptions of the DISCO App (1 = strongly disagree; 5 = strongly agree). Descriptive statistics summarized results and mean comparisons were used to assess perceptions by patient self-identified race. Results: Of the 202 patients recruited, 124 were randomized to the intervention arm (67 Black patients; 57 White patients). All patients completed using the DISCO App prior to their provider entering the exam room and 80% of patients needed 15 minutes or less to use the DISCO App, with no difference by patient race. Black patients ( M = 4.4) reported finding the DISCO App more helpful than White patients ( M = 3.9; p = .02) and it brought up cost issues they had not considered (Black patients = 3.5; White patients = 3.0; p = .05). Patients reported the questions were easy to understand ( M = 4.4), helped them feel it was okay to talk with their provider about cost ( M = 4.0), that it prompted cost questions ( M = 3.3), that they learned what costs to consider (55%), and learned ways to manage cost (62%) with no differences by patient race. Conclusions: The DISCO App was feasible and acceptable to Black and White patients with cancer, with Black patients reporting more favorable perceptions than White patients. Next steps include assessing effectiveness in improving outcomes including prompting patient-provider treatment cost discussions and related financial toxicity outcomes (e.g., treatment adherence). Clinical trial information: NCT04766190 .

9557 Background: High-dose interleukin-2 (IL-2) is administered following tumor-infiltrating lymphocyte (TIL) therapy, yet cardiotoxicity frequently limits dose delivery. The clinical significance of peri-dose troponin elevations during IL-2 remains poorly defined. We evaluated troponin kinetics during IL-2 dosing and their association with significant cardiac events and IL-2 interruption. Methods: We retrospectively analyzed patients with metastatic melanoma treated with TIL therapy followed by inpatient high-dose IL-2 at Mayo Clinic Rochester (N = 24; 87 IL-2 doses). High-sensitivity troponin and ECGs were obtained before and after each IL-2 dose. Clinically significant cardiac events were defined as QTc prolongation > 480 ms, arrhythmias (excluding isolated sinus tachycardia), new ECG abnormalities, vasopressor requirement, or cardiology consultation. Dose-level outcomes included cardiac events and subsequent IL-2 dose interruption. Paired troponin changes were assessed using Wilcoxon signed-rank testing. Dose-level associations were evaluated using clustered logistic regression to account for repeated IL-2 doses within patients. Results: 24 patients received 87 IL-2 doses (median 3 [IQR 2 - 5]). Median age was 63 years (IQR 54 - 70), and 58% were male. Baseline troponin median was 11 ng/L (IQR 6 - 21); 38% had baseline troponin > 14 ng/L. Post-dose troponin exceeded 14 ng/L in 16/24 patients (67%) and 48/87 doses (52%). Median delta troponin was 0 ng/L (IQR −1 to 6; range −24 to 133), with post-dose levels higher than pre-dose values ( p = 0.02). Clinically significant cardiac events occurred in 33% of patients; no post-IL-2 reductions in left ventricular ejection fraction were observed. At the dose level, cardiac events occurred only when post-dose troponin exceeded 14 ng/L (15/48 [31%] vs 0/39 doses; p < 0.001). In clustered logistic regression, post-dose troponin ≥15 ng/L was independently associated with cardiac events (OR 9.6, 95% CI 1.5 - 60.6; p = 0.02) and subsequent IL-2 dose interruption (OR 3.4, 95% CI 1.1 - 10.7; p = 0.04). When modeled continuously, each 1-unit increase in log-transformed post-dose troponin was associated with higher odds of cardiac events (OR 3.3, 95% CI 1.6 - 6.7; p = 0.001) and IL-2 interruption (OR 2.8, 95% CI 1.6 - 4.9; p < 0.001). Baseline troponin correlated with peak post-dose troponin (ρ = 0.44, p = 0.04). Conclusions: Peri-dose troponin elevations are common during post-TIL high-dose IL-2; however, higher post-dose troponin independently identifies clinically significant cardiac toxicity and predicts IL-2 interruption after accounting for repeated dosing within patients. Baseline troponin modestly predicts peak elevations, supporting standardized, risk-stratified troponin monitoring and prospective evaluation of toxicity-adaptive IL-2 delivery strategies in TIL therapy.

5068 Background: 177 Lu-PSMA-617 (LuPSMA) is a groundbreaking therapy for mPC, but biomarkers are urgently needed to improve patient selection. Plasma-derived EVs are emerging blood-based markers of tumor burden. Here, we analyzed levels of EVs of 123 patients (pts) from 4 cohorts: a pre- and during LuPSMA treatment for a contemporary prospective Mayo Clinic cohort, pre-treatment plasma levels of EVs for a historical Tulane cohort, localized prostate cancer (LPC) after radical prostatectomy (RP), and male healthy donors (HD). Methods: Blood samples were collected from 51 pts pre-cycles (pre-C) 1-3 of LuPSMA at Mayo Clinic from 12/2024-12/2025 and 26 pts pre-C1 at Tulane Cancer Center between 12/2018-1/2025. Small and large EVs were incubated with fluorescently conjugated antibodies (PSMA, STEAP1, CEACAM5, and TROP2) and enumerated using nanoscale flow cytometry. EVs from blood samples of 10 HD and 36 LPC post-RP from 6/2020-8/2024 at Mayo Clinic as controls. AUC-ROC and logistic regression analyses were performed to identify marker signatures associated with PSA50 response. Results: Baseline demographics are shown in the table. Median levels of PSMA, STEAP1, CEACAM5, and TROP2 EV/milliliter (mL) were all significantly higher for pts with mPC (pooled Tulane and Mayo cohorts) compared to LPC post-RP (p<0.001) and HD (p<0.001). In the Mayo cohort, 10 of 51 pts (20%) had undetectable PSA pre-C1. There were no significant differences in median pre-C1 plasma EV levels for these 4 different types of EVs comparing pts with undetectable vs detectable PSA. For 41 Mayo pts with detectable PSA pre-C1, 20 achieved PSA50 response at time of data cutoff (49%), while 7 pts (17%) had persistent PSA rise on LuPSMA. For pts who achieved PSA50, there was a significant decline in both CEACAM5 and TROP2 EVs/mL pre-C1 compared to pre-C3 (19 x 10 6 vs 5.8 x 10 6 , p=0.003 and 16 x 10 6 vs 5.5 x 10 6 , p<0.001, respectively), while no significant changes occurred for the 7 pts with no PSA response. A composite score of pre-C1 CEACAM5 and TROP2 EVs (large- and small-sized EVs) demonstrated the strongest association with PSA50 response (OR=2.96, 95% CI: 1.27-6.44, p=0.038), achieving AUC of 0.73. PSMA and STEAP1 EVs did not show any significant changes from pre-C1 to pre-C3. Conclusions: Plasma-derived EVs are a promising biomarker to identify patients who will benefit from LuPSMA. Longer follow-up and enrolling a larger cohort are underway. Clinical trial information: NCT06200103 . Median values for pre-LuPSMA (Mayo and Tulane), post-RP for LPC, and HD. Mayo mPC (n=51) Tulane mPC (n=26) LPC (n=36) HD (n=10) Age (range) 73 (57-87) 71 (54-83) 66 (56-77) 55 (50-57) Prior lines (range) 1 (1-3) 4 (1-11) - - Gleason score 9 8 7 - PSA (range) 1.0 (0-182) 75 (0.8-503) - - PSMA EV/mL 3.7 x 10 6 14 x 10 6 2.0 x 10 6 1.4 x 10 6 STEAP1 EV/mL 30 x 10 6 45 x 10 6 12 x 10 6 12 x 10 6 CEACAM5 EV/mL 17 x 10 6 5.1 x 10 6 3.7 x 10 6 3.9 x 10 6 TROP2 EV/mL 13 x 10 6 5.2 x 10 6 4.5 x 10 6 3.6 x 10 6

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 (%).