636 Background: In NIAGARA (NCT03732677), addition of perioperative D to neoadjuvant chemotherapy (NAC) and radical cystectomy (RC) demonstrated a significant improvement in event-free survival (EFS) and overall survival and a numerical increase in pathological complete response (pCR) vs NAC and RC alone in pts with MIBC. In a prior exploratory analysis, negative plasma ctDNA status after neoadjuvant treatment prior to RC (pre-RC) was associated with prolonged EFS but not pCR. Here we assess utDNA as a complementary approach in this setting. Methods: Cisplatin-eligible pts with MIBC (cT2-T4aN0/1M0) were randomized 1:1 to receive perioperative D plus NAC (cisplatin + gemcitabine) and RC (D arm) or NAC and RC alone (comparator [C] arm). Dual primary endpoints were EFS and pCR. Exploratory analysis of utDNA and ctDNA was completed using the personalized Signatera assay (Natera, Inc, Austin, TX, USA) at baseline (BL; n=205) and pre-RC (n=183). Results: Of 1063 pts, 265 (25%) comprised the biomarker-evaluable population (BEP; 134 D arm; 131 C arm). At BL, lower utDNA levels were associated with longer EFS (low vs high utDNA HR 0.65, 95% CI 0.40−1.04). From BL to pre-RC, utDNA+ rate decreased from 85% to 55%. utDNA clearance was associated with longer EFS (HR 0.24, 95% CI 0.09−0.62) and was 12% higher in the D vs C arm (39% vs 27%). Pre-RC utDNA status was associated with a pCR (utDNA−; 72% [55/76] vs utDNA+; 18% [17/96]). Pre-RC utDNA and ctDNA status differentially correlated with disease stage at RC, with utDNA+ correlating with noninvasive disease (Conclusions: This analysis suggests that lower BL levels and pre-RC clearance of utDNA are associated with better EFS and shows the addition of D to NAC increased utDNA clearance. utDNA status at pre-RC was more closely associated with pCR vs prior findings for ctDNA status. Combined pre-RC ctDNA and utDNA analysis was associated with EFS and may provide complementary insights into disease stage at RC. utDNA status could provide clinically relevant information on the primary bladder tumor, particularly in ctDNA− pts, highlighting the potential value of combining utDNA and ctDNA to inform future management of MIBC. Clinical trial information: NCT03732677 . Pre-RC utDNA and ctDNA correlation with disease stage a at RC. Status n T0N0M0 (%) ≥T2N0M0 (%) T any N+ M+ (%) ctDNA− utDNA− 72 73.6 12.5 12.5 1.4 ctDNA− utDNA+ 62 24.2 30.7 37.1 8.1 ctDNA+ utDNA− 6 16.7 0.0 0.0 83.3 ctDNA+ utDNA+ 33 6.1 0.0 48.5 45.5 a By locally collected pathological assessment.

PURPOSE:HER2 targeting is increasingly relevant in metastatic urothelial cancer (mUC) because of emerging antibody-drug conjugates, in which assessment of tumor HER2/ERBB2 status could aid interpretation of ongoing trials. We evaluated whether precise ERBB2 genotype can be determined from mUC ctDNA and the relationship with tissue status. EXPERIMENTAL DESIGN:ERBB2 genotype was determined through targeted sequencing of longitudinal samples from 226 patients with mUC. Heterogeneity was evaluated across ctDNA and metachronous tumor tissue ERBB2 genotype and compared with HER2 IHC. RESULTS:Activating ERBB2 mutation and/or amplification was identified in 16% and 29% of patients by ctDNA and tissue sequencing, respectively. Alternatively, 55% of tissue samples were HER2 IHC positive. Agreement between HER2 IHC and ERBB2 genotype (by either ctDNA or tissue) was 64%, in contrast to 87% between patient-matched ctDNA and tissue genotypes. Across serial samples, genotype and IHC revealed marked heterogeneity in ERBB2 status. Factors linked with heterogeneity included ERBB2 amplifications on extrachromosomal DNA, detected through whole-genome sequencing of ctDNA and FISH, and subclonal ERBB2 mutations, which were evident in half of ctDNA and one-third of tissue samples. CONCLUSIONS:We report a combined analysis of HER2 IHC and ERBB2 genotype in mUC ctDNA and archival tissue, revealing high spatiotemporal heterogeneity. Our data suggest that sole reliance on DNA- or protein-based HER2 assessment is insufficient to capture nuanced genomic indicators of HER2 pathway reliance and support a role for ctDNA alongside existing methods for characterizing HER2/ERBB2 status during biomarker development in mUC.

INTRODUCTION:Approximately 25% of patients diagnosed with bladder cancer have muscle-invasive disease (MIBC). While real-world data have highlighted opportunities to improve curative-intent treatment rates, comprehensive population-level data in Canada are limited. This study aimed to assess patterns of care and outcomes in a real-world cohort of MIBC in Canada. METHODS:This retrospective, observational study describes baseline characteristics, treatment patterns, and overall survival (OS) of individuals with de novo MIBC diagnosed between 2010 and 2020 in Alberta, Canada. Data from adult patients with MIBC (T2-T4, N0/1, M0) were obtained from administrative databases and analyzed using basic statistics, multivariate regression analyses, and the Kaplan-Meier method. RESULTS:We identified 1292 patients with de novo MIBC. Of these, 76% were male with a median age of 73 years, 68% had cT2, and 76% had cN0 disease; approximately half had a Charlson comorbidity index (CCI) ≥1. Overall, 25% did not receive active treatment, while 58% received curative-intent treatment (49% underwent radical cystectomy [RC] and 9% received chemoradiotherapy), and 17% received some form of non-curative-intent treatment. Of those who underwent RC, 45% received neoadjuvant chemotherapy (NAC). Median overall survival (mOS) in the entire cohort was 2.1 years (95% confidence interval 1.9-2.4). Key predictors of inferior survival were age ≥76 years, CCI score of ≥1, T4 tumor stage, or not receiving NAC. CONCLUSIONS:This real-world analysis highlights opportunities to improve outcomes for patients with MIBC. Increasing access to curativeintent treatments, particularly in the elderly and those with comorbidities, is likely to enhance patient care and outcomes.

INTRODUCTION:Approximately three-quarters of patients newly diagnosed with bladder cancer have non-muscle-invasive disease (NMIBC). Among these patients, those with high-risk (HR) features should be managed more aggressively in an attempt to circumvent the elevated risk of recurrence/progression. Population-based data on the incidence of HR-NMIBC and receipt of guideline-recommended care are limited. METHODS:This retrospective, observational study gathered data from multiple linked provincial (Alberta) healthcare databases to describe baseline characteristics, treatment patterns, and survival outcomes in a population of individuals diagnosed with HR-NMIBC from 2010-2020. Data for all patients aged >18 years with T1, Tis, or high-grade Ta NMIBC ("high-risk") were analyzed using basic statistics, multivariate regression analyses, and the Kaplan-Meier method. RESULTS:Of 6837 de novo NMIBC patients identified, 3874 (57%) were categorized as HR-NMIBC. The majority (82%) were male with a median age of 72 years, and approximately half had a Charlson comorbidity index score ≥1. Following initial transurethral resection of bladder tumor (TURBT), 61% of the cohort received no adjuvant bacillus Calmette-Guérin (BCG) or chemotherapy, while 36% received BCG, 3% gemcitabine, and 1% mitomycin C. Patients underwent a median of four TURBT procedures. 'Adequate BCG' (≥5 induction doses + ≥2 maintenance doses) was received by 32% of BCG-treated and 12% of all HR-NMIBC patients. Survival was improved in patients receiving adequate BCG. CONCLUSIONS:Data from this large, real-world population highlights poor use of induction/maintenance BCG therapy following TURBT among patients with HR-NMIBC.

BACKGROUND:Metastatic castration-resistant prostate cancer (mCRPC) has a poor prognosis, necessitating the investigation of novel treatments and targets. This study evaluated JNJ-70218902 (JNJ-902), a T-cell redirector targeting transmembrane protein with epidermal growth factor-like and 2 follistatin-like domains 2 (TMEFF2) and cluster of differentiation 3, in mCRPC. PATIENTS AND METHODS:Patients who had measurable/evaluable mCRPC after at least one novel androgen receptor-targeted therapy or chemotherapy were eligible. Participants received subcutaneous JNJ-902 0.3, 1.0, 1.5, 3.0, or 6.0 mg once weekly (QW) or 2.0, 3.0, 4.0, or 6.0 mg biweekly (Q2W). Study objectives included assessment of safety, pharmacokinetics, immunogenicity, and preliminary efficacy. RESULTS:Eighty-two participants were enrolled to receive at least one dose of JNJ-902 (QW; n = 38; Q2W; n = 44). Median duration of treatment was 1.91 (0.0-19.4) months across dosing groups. All participants experienced at least one treatment-emergent adverse event (TEAE) and 76 (92.7%) experienced treatment-related TEAEs. Fourteen participants (17.1%) experienced a TEAE that led to study discontinuation, of which 3 (3.7%) were related to JNJ-902. Dose-limiting toxicities were observed in 2 participants (2.4%). Five participants (15.2%) with measurable disease had a confirmed partial response and 10 participants (12.2%) had ≥50% decrease from baseline prostate-specific antigen levels. Clinical activity was not dose related and no clear exposure-response relationship was observed. CONCLUSIONS:In this study, dose escalation was limited by emerging dose-limiting toxicities. Although a recommended phase II dose was not determined, findings indicate TMEFF2 to be a potential target in mCRPC that warrants further investigation.

Purpose Chemotherapy is the primary treatment for metastatic nonseminomatous germ cell tumors (mNSGCTs), but patients often encounter postchemotherapy residual disease. Accurate noninvasive methods are needed to predict the histology of these masses, guiding treatment and reserving surgery for those with teratoma. This study aims to enhance predictive accuracy by integrating computed tomography (CT) radiomics features with miRNAs (miR371-375) to distinguish between teratoma and nonteratoma histology in postchemotherapy residual masses. METHODS We retrospectively identified 111 lesions, divided into training and test sets (n = 78 v 33) with equal class distribution. 3D Slicer was used to segment lesions with a short axis of >10 mm from the postchemo-presurgical CT images, and radiomics features were extracted. Presurgery plasma miR371-375 levels were measured by real-time polymerase chain reaction. Four machine learning models evaluated the predictive value of radiomics alone (R-only) and combined with miR371-375 levels, and the best performer was selected. Clinical factors associated with teratoma from univariate analysis were included in multivariate analysis with the best radiomics signature to assess their impact on predicting teratoma histology. Results The CatBoost (CB) model R + 371 + 375 exhibited the best and most robust overall accuracy for predicting residual teratoma, with the highest AUC values (0.96, 95% CI, 0.88 to 1.0 for training, 0.83, 95% CI, 0.68 to 0.98 for testing) and a well-balanced sensitivity and specificity. Univariate analysis identified presurgery alpha-fetoprotein (P = .01), beta-human chorionic gonadotropin (P = .01), initial teratoma pathology (P = .01), and lymph node metastases (P = .02) as significant predictors for teratoma. Multivariate analysis included these features and the radiomics signature, which was the strongest independent predictor (P < .0001). Conclusion Combining miR371-375 with CT radiomics features improves the accuracy of predicting teratoma histology of postchemotherapy residual disease in mNSGCTs and, therefore, has the potential to guide treatment decision making.

Clonal hematopoiesis (CH) is an age-related expansion of white blood cell (WBC) progenitors linked to risk of hematological malignancy. Patients with cancer have increased CH prevalence compared to healthy populations, but the characteristics and relevance of CH in advanced urological cancers are unknown. We interrogated CH and circulating tumor DNA (ctDNA) in 299 patients with metastatic urothelial or renal cell carcinoma using error-corrected targeted sequencing of matched WBC DNA and plasma cell-free DNA (cfDNA). 73% of patients carried CH variants at ≥0.25% allele frequency, with 13% exhibiting large CH populations marked by variants ≥10%. CH presence, clone size, and genotype did not impact patient survival. However, CH variants frequently affected solid cancer driver genes and were not individually discriminable from ctDNA variants based on cfDNA features including fragment length. In contrast, matched WBC DNA sequencing to ≥25% of cfDNA depth sufficiently resolved CH from ctDNA variants. Serial profiling revealed ctDNA and CH temporal dynamics including treatment-related expansion of PPM1D-mutated CH clones following platinum chemotherapy. Our data reveal the molecular landscape of CH in urological cancers and suggest that CH interferes in clinical ctDNA genotyping. We urge test providers to comprehensively filter CH from ctDNA results using matched WBC sequencing and propose a cost-effective framework for its integration into existing plasma-only assays.

PURPOSE:We investigated whether metformin decreases metabolic syndrome (MS) risk in patients with prostate cancer (PCa) receiving androgen deprivation therapy (ADT). MATERIALS AND METHODS:In this phase 3, multicenter, double-blind, randomized controlled trial, normoglycemic patients with PCa planned for at least 9 months of ADT were randomized 2:1 to receive metformin 850 mg or placebo twice daily orally for 18 months. The primary objective was to compare proportions of MS at 18 months between the study arms. RESULTS:Between July 2018 and November 2023, 166 patients were randomized. The trial closed prematurely on November 24, 2023, because of drug supply cessation and the planned enrollment numbers (n = 300) were not met. A total of 90 (metformin) and 45 patients (placebo) were analyzed in the final analysis. The median follow-up was 24 months (IQR: 19.5-36 months). Proportions of MS between metformin and placebo arms were 38/90 (42%) vs 26/45 (58%) at baseline (P = .09) and 40/73 (55%) vs 23/34 (68%) at 18 months (P = .2). Significant reductions in mean (SD) body weight occurred with metformin at 9 (-0.9 [4] vs +1.8 [3.8] kg; P < .001) and 12 months (-0.33 [3.9] vs +1.8 [3.9] kg; P = .004). Mean (SD) hemoglobin A1c was lowered with metformin at 9% (-0.02% [0.23%] vs +0.08% [0.26%]; P = .02) and 12 months (+0.03% [0.27%] vs +0.08% [0.27%]; P = .03). Significantly smaller increments in mean (SD) waist circumferences were noted with metformin at 9 (+0.8 [4.3] vs +2.9 [5.7] cm; P = .03), 12 (+1.9 [5.1] vs +3.3 [6] cm; P = .15), and 18 months (+1.8 [3.8] vs +3.8 [6.1] cm; P = .03). CONCLUSIONS:Metformin did not reduce the risk of MS in patients with PCa on ADT. However, significant improvements in body weight, waist circumference, and hemoglobin A1c suggest a potential role for metformin in reducing ADT-related complications.

647 Background: The primary treatment of most mNSTC is chemotherapy followed by surgery if the residual disease (RD) is >1 cm. However, conventional imaging lacks the specificity to characterize the tissue, often leading to overtreatment. This study hypothesizes that integrating CT-driven radiomics features with plasma miR371 and miR375 will enhance the predictive accuracy of Machine Learning (ML) models to predict teratoma, viable germ cell (vGCT) and fibrosis/necrosis (F/N) in mNSTC patients with RD. Methods: 111 lesions from52 patients, including residual teratoma (n=57), F/N (n=33), vGCT (n=10), and additional seminoma (n=11) for training purposes were included, split into training (N=78) and test cohorts (N=33). Lesions were lymph nodes (n=87), lung (n=21), and brain (n=3) with a median size of 1.6 cm (Q1-Q3 interval=1.2-2.73 cm). 3D Slicer version 5.6.1 was used to segment the RD > 1 cm (short axis) and extract radiomics features. Plasma miRNA levels before resection were measured by RT-PCR. Random Forest (RF), Support Vector Machine (SVM), Gradient Boosting (GB), and CatBoost (CB) ML models were evaluated to define the operating characteristics of radiomics alone (R-only) and in combination with miR371 (371) and/or miR375 (375) levels in predicting teratoma, vGCT and F/N. Results: For predicting teratoma, the best models were RF (R+375 and R+371+375), CB (R+371+375), and GB (R+371 and R+371+375). While adding miR371 or miR375 to R-only slightly improved AUC across models, the best results were achieved with the R+375+371 dataset. CB achieved AUCs ranging from 0.94 to 0.97 in training and 0.81 to 0.93 in test sets, with its highest AUC of 0.93 (95% CI: 0.78-0.97) on the R+375+371 dataset to differentiate all three classes. Similarly, GB demonstrated strong performance, achieving its highest AUC of 0.93 (95% CI: 0.79-0.96) on the R+375+371 dataset (Table). Conclusions: Integration of plasma miR371, miR375 and radiomics improved accuracy of predicting histologies across all ML models. These methods could be used to characterize the histology of RD in mNSTC patients to better inform treatment decisions. Further refinement, including incorporation of histological findings of the primary tumor, will be reported. AUC values of different ML algorithms on training and test sets. TRAINING SET TEST SET Model ±SD R R+375 R+371 R+375+371 Model (95% CI) R R+375 R+371 R+375+371 RF 0.93±0.05 0.95±0.04 0.95±0.03 0.96±0.04 RF 0.8(0.59-0.89) 0.85(0.72-0.93) 0.87(0.76-0.95) 0.91(0.78-0.95) SVM 0.84±0.06 0.84±0.09 0.89±0.11 0.89±0.09 SVM 0.72(0.54-0.80) 0.74(0.56-0.82) 0.83(0.69-0.92) 0.84(0.76-0.94) GB 0.94±0.04 0.91±0.08 0.95±0.05 0.97±0.03 GB 0.84(0.61-0.96) 0.89(0.77-0.97) 0.89(0.79-0.96) 0.93(0.79-0.96) CB 0.95±0.03 0.94±0.03 0.94±0.04 0.97±0.03 CB 0.81(0.6-0.93) 0.86(0.73-0.94) 0.89(0.78-0.97) 0.93(0.78-0.97)

662 Background: Activating alterations in FGFR3 (most commonly S249C) occur in 15-20% of metastatic urothelial cancers (mUC) and <5% in other solid tumors. Erdafitinib, a pan FGFR1-4 inhibitor, improves survival in 2L FGFR3 -altered mUC but has dose limiting toxicities (DLTs) driven by off-target FGFR1/2/4 inhibition. LY3866288 is an oral, potent, isoform-selective, small molecule FGFR3i designed to limit off-target toxicities with preserved activity against acquired FGFR3 resistance mutations. Here we report initial clinical data from the phase 1 dose escalation cohort of LY3866288in FGFR3 -altered advanced solid tumors. Methods: Adults with advanced or metastatic solid tumors with an FGFR3 or FGFR3 ligand alteration (tumor or blood) that progressed on available standard therapies, ECOG PS ≤1, and RECIST v1.1 evaluable (including non-measurable) disease were eligible. Dose escalation used a single-patient accelerated design followed by mTPI-2 method. Key endpoints were safety, PK, and antitumor activity. Serial plasma samples were collected for ctDNA analysis. Results: As of 27 Aug 2024, 101 patients (pts) were treated at 10 dose levels (DLs) of LY3866288 (6 mg QD – 400 mg BID). Median age was 67 (range, 26-93), 69% ECOG PS 1, and 70% had mUC. Median lines of prior therapy was 3 (range, 1-9), including prior FGFRi in 23%. LY3866288 consistently demonstrated trough concentrations that exceeded IC 90 for FGFR3 S249C at DLs ≥200 mg BID. No significant differences in exposures were observed in pts with moderate renal insufficiency (eGFR 30-49 ml/min). No DLT was observed at any DL. At DLs ≥200 mg BID, the most common treatment-emergent AEs (TEAEs) were diarrhea (67%), hyperphosphatemia (28%), fatigue (23%), increased ALT (22%), and AST (22%); most (68%) TEAEs were grade 1/2. TEAEs associated with poor tolerance and compliance to erdafitinib (retinopathy, onycholysis, and hand-foot syndrome) were ≤5% and low grade. Treatment-related AEs (TRAEs) led to dose reduction in 5% of pts and none were associated with discontinuation. In mUC pts with an activating mutation/fusion dosed at ≥200 mg BID, the objective response rate (ORR) was 42% (14/33; 10 confirmed as of 6 Sep 2024, 4 ongoing and pending confirmation); responses were observed in both mutations (Y373C, S249C, R248C, S371C) and fusions (TACC3). In mUC pts previously treated with an FGFRi, the ORR was 45% (5/11). One pt each with NSCLC (S249C) and biliary tract cancer (TACC3) also achieved a PR. 14/16 PRs (88%) are ongoing. Decreases in FGFR3 ctDNA VAF occurred in 12/13 pts (92%) with available results at cycle 2 or 3, of which 8 achieved clearance (5 with PR; 3 with SD). Conclusions: LY3866288 is well-tolerated with robust clinical activity at multiple DLs, including in erdafitinib refractory mUC. Randomized dose optimization is ongoing and updated results will be presented. Clinical trial information: NCT05614739 .

TPS890 Background: Neoadjuvant therapy (NAT) followed by radical cystectomy (RC) is the standard of care for muscle-invasive bladder cancer (MIBC). Approximately 35-40% of patients have no residual cancer at the time of surgery, suggesting that these patients could potentially avoid definitive bladder treatments (DBT), including RC or trimodal therapy (TMT). However, the current clinical tools used to detect residual disease prior to cystectomy are inadequate. The question remains whether patients with complete response (CR) require DBT or if active surveillance (AS) could be a safe alternative. The NEO-BLAST trial investigates whether a combination of bladder MRI, circulating tumor DNA (ctDNA), urinary tumor DNA (utDNA) and transurethral bladder tumor resection (TURBT) can accurately identify MIBC patients with a clinical CR (cCR) following NAT, and whether AS is non-inferior to standard of care (SOC) in those who achieved cCR. Methods: This is a multicenter, phase II/III, non-inferiority open-label clinical trial that will randomize patients with MIBC who achieve cCR after NAT to AS versus SOC DBT, including either RC or trimodal therapy (TMT) (NCT06537154). The primary endpoint is feasibility of randomization for the phase II pilot-RCT, and metastasis-free survival (MFS) at two years for the phase III. Eligible patients will be adults with non-metastatic MIBC (≥T2, N0M0) who are candidates to SOC NAT followed by DBT as per the current practice. After enrolment, ctDNA and utDNA will be collected. Only participants who complete SOC NAT will then undergo a comprehensive clinical restaging process, including repeat ctDNA and utDNA, bladder mpMRI, urine cytology, and TURBT with template biopsies. Participants meeting criteria for cCR, defined as negative ctDNA, utDNA, MRI, and TURBT, will be randomized to either AS-arm or DBT-arm, while those without cCR will receive SOC. Participants will be monitored with cystoscopy and urine cytology (if bladder in situ) every three months for 2 years, along with ctDNA and imaging at 3, 6, 12, 18, and 24 months. The pilot-RCT will plan to enrol 72 patients, and if 25% is found to have cCR and accept to be randomized, the trial will be considered feasible. Assuming a 5% event rate at 2 years (MFS) in both groups and a type I error of 5% (1-sided), 78 per group will provide 80% power to reject the hypothesis of inferiority. We anticipate enrolling 688 patients for the phase 3 to have a total of 172 patients with cCR randomized, assuming 10% lost to follow-up. An independent Data Monitoring Committee will oversee safety and efficacy throughout the trial. Clinical trial information: NCT06537154 .

Hintergrund: Die leptomeningeale Karzinomatose ist ein außergewöhnlich seltenes Metastasenmuster bei Urogenitaltumoren, das in weniger als 0,1% der Fälle beschrieben wird. Wir berichten über 2 Fälle von Patienten mit metastasiertem Urothelkarzinom, die zunächst auf Enfortumab Vedotin (EV) ansprachen, bevor sie leptomeningeale Metastasen entwickelten. Falldarstellung: Fall 1: Bei einem 55-jährigen Mann wurde ein metastasiertes Urothelkarzinom diagnostiziert. Er wurde zunächst mit einer Chemotherapie mit Cisplatin/Gemcitabin behandelt, gefolgt von Pembrolizumab als Zweitlinientherapie, wobei unter beiden Therapien eine Progression eintrat. Es wurde bei ihm mit einer EV-Therapie begonnen und er sprach partiell anhaltend auf sie an. Nach 12 Behandlungszyklen entwickelte er neurologische Symptome, wobei sich in der Bildgebung umfangreiche leptomeningeale Metastasen zeigten. Eine Lumbalpunktion wurde durchgeführt, wobei die Zytologie positiv auf ein metastasierendes Karzinom ausfiel. Fall 2: Bei einem 63-jährigen Mann wurde ein metastasiertes Urothelkarzinom diagnostiziert. Er erhielt 6 Zyklen Chemotherapie mit Platin/Gemcitabin, gefolgt von einer Avelumab-Erhaltungstherapie, woraufhin sich bei ihm radiologisch eine Progression entwickelte. Bei ihm wurde mit einer EV-Therapie begonnen, auf die er radiologisch komplett ansprach. Nach 13 Behandlungszyklen entwickelte er neurologische Symptome und in der Bildgebung zeigte sich eine ausgedehnte leptomeningeale Erkrankung. Die Zytologie bestätigte ein metastasiertes Urothelkarzinom. Schlussfolgerung: Dieses ungewöhnliche Ausbreitungsmuster, das bei 2 Patienten beobachtet wurde, die kurz hintereinander mit EV behandelt wurden, stellt ein potenziell signifikantes und neues Progressionsmuster innerhalb dieser Population dar.

Predictive biomarkers of response to immune checkpoint-based therapies (ICI) remain a critically unmet need in the management of advanced renal cell carcinoma (RCC). The complex interplay of the tumour microenvironment (TME) and the circulating immune response has proven to be challenging to decipher. MicroRNAs have gained increasing attention for their role in post-transcriptional gene expression regulation, particularly because they can have immunomodulatory properties. We evaluated the presence of immune-specific extracellular vesicle (EV) microRNAs in the plasma of patients with metastatic RCC (mRCC) prior to initiation of ICI. We found significantly lower levels of microRNA155-3p (miR155) in responders to ICI, when compared to non-responders. This microRNA has unique immunomodulatory properties, thus providing potential biological rationale for our findings. Our results support further work in exploring microRNAs as potential biomarkers of response to immunotherapy.

Abstract Introduction: Clonal hematopoiesis (CH) is an age-related process whereby hematopoietic progenitor cells with specific mutations gain a proliferative advantage, resulting in populations that can be detected in blood. CH is a major confounder in plasma cell-free DNA (cfDNA) assays that do not profile patient-matched white blood cell (WBC) DNA to distinguish circulating tumor DNA (ctDNA) somatic mutations from those with hematopoietic origin. We aimed to characterize CH in patients with advanced urologic cancers and clarify the potential for CH to interfere with plasma-based tumor genotyping. Methods: We applied error-corrected targeted DNA sequencing (median 2200X) to matched cfDNA and WBC DNA from 301 patients with advanced urothelial cancer (UC) or renal cell carcinoma (RCC) enrolled in a provincial biobank, using a 57 gene panel capturing key CH and urologic cancer genes. CH mutations were defined as those detected in both WBC and cfDNA with a variant allele frequency (VAF) exceeding a 0.25% limit of detection and supported by at least 5 mutant reads. In contrast, ctDNA mutations were required to be exclusively detected in plasma, with a cfDNA VAF ≥5 times the VAF in WBC. Results: 73% (221/301) of patients had ≥1 CH mutation with a VAF above 0.25% (35% of patients had a variant above 2% VAF), and CH- patients were younger than CH+ (RCC: 56 vs 68.5, p<0.01; UC: 63 vs 72, p<0.01). There was no difference in CH prevalence by biological sex. There was no difference in overall survival according to CH status (UC: [CH+] 13 vs [CH-] 16 months, p=0.98; RCC: [CH+] 33 vs [CH-] 49 months, p=0.77), in contrast to the presence of ctDNA mutations which is an established prognostic factor linked with shorter overall survival (UC: [ctDNA+] 10 vs [ctDNA-] 23 months, p<0.01; RCC: [ctDNA+] 15 vs [ctDNA-] 49 months, p<0.01). CH+ patients carried CH mutations most commonly within hematologic malignancy-associated genes (e.g. DNMT3A [58%] and TET2 [26%]), although genes linked to DNA damage response such as TP53 (10%) and ATM (9%) were also mutated. PPM1D was mutated more frequently in UC compared to RCC within CH+ patients (UC: 22%, RCC: 9%, p<0.01), likely attributable to platinum chemotherapy exposure prior to blood collection in 50% of the UC cohort. Importantly, a notable proportion of mutations in UC- or RCC-relevant driver genes originated from CH rather than cancer, including 28% and 65% of mutations falling in TP53 and ATM, respectively. Finally, randomly downsampling sequencing reads from WBC DNA suggested that 500X coverage is sufficient to resolve 90% of CH events with >1% VAF. Conclusion: CH was highly prevalent in patients with advanced urologic malignancies but had no impact on survival in this heterogeneous real-world cohort. CH commonly affected clinically-relevant driver genes that are also altered in solid cancers, potentially causing false-positive genotyping and inflating tumor mutation burden estimates in plasma-only ctDNA assays. Incorporating WBC sequencing to liquid biopsy assays can help correctly identify tumor-originating mutations. Citation Format: Aslı D Munzur, Jack V W Bacon, Francine Fishbein, Gráinne Donnellan, Cecily Q Bernales, Karan Parekh, Gillian Vandekerkhove, David C Müller, Cameron Herberts, Lucia Nappi, Corinne Maurice-Dror, Kim N Chi, Bernhard J Eigl, Christian Kollmannsberger, Maryam Soleimani, Alexander W Wyatt. Prevalence and clinical relevance of clonal hematopoiesis in metastatic urologic malignancies [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr B064.

e16608 Background: Although available data supports trimodal therapy (TMT) as a bladder sparing treatment for MIBC with outcomes comparable to cystectomy, uptake in Canada is low. A retrospective evaluation in British Columbia, Canada, was undertaken to evaluate real-world outcomes in MIBC patients (pts) undergoing bladder sparing radiotherapy (RT). Methods: MIBC pts were identified from the BC Cancer registry who received RT with curative intent between Jan 1, 2002, and Dec 31, 2020. Disease free survival (DFS), overall survival (OS), and disease specific survival (DSS) were calculated for those receiving RT versus combined modality treatments. Further analysis was undertaken to identify factors associated with outcomes. Results: The population was 231 pts, predominantly male (74%), median age 81 (range: 44-95). Almost all (97%) presented with high-grade MIBC, and 67.1% had an ECOG score of 0-1. The reasons for bladder preservation were frailty/comorbidities (77.1%), pt preference (16%) and inoperability (6.9%). 170 (73.6%) pts underwent RT alone; the remainder were treated with chemoRT (16.5%), neoadjuvant chemotherapy (nCT)+RT alone (5.6%), nCT+chemoRT (3%), chemoRT+adjuvantCT (0.9%), and RT+adjuvantCT (0.4%). The median OS in the RT-only group (25.2 months, 95% CI, 19.5-31) was significantly lower than for chemoRT (39.7 months, 95% CI, 13.5-65.9, p=0.013). Pts who underwent maximal transurethral resection of the bladder tumor (TURBT) in the chemoRT group exhibited significantly prolonged OS (56.5 vs. 31.9 months, p=0.006). Pts with maximal TURBT who had a second TURBT while waiting for RT demonstrated a significant improvement, compared to those with a second TURBT due to submaximal TURBT (59.3 vs. 13.3 months, p<.001). Despite these findings, DSS analysis did not show statistically significant differences between the treatment groups (p=0.38), even when stratified by maximal TURBT (p=0.207). Similarly, the median DFS did not represent a difference between the groups (26.6 vs. 22.2 months, p=0.772). Cox regression analysis revealed the absence of carcinoma in situ trended towards a decreased risk of death (HR: 0.52, p<0.001), as did the absence of hydronephrosis (HR: 0.65, p=0.009) and an increase in the total number of RT fractions (HR: 0.92, p=0.001). In the analysis of treatment modalities (RT vs. chemoRT), there was a significant difference in the distribution of recurrence sites (Chi-Square=4.15, p=0.04). Local recurrences were identified less frequently in the chemoRT group. Conclusions: This population-based study showed notable demographic and treatment-related characteristics that influenced OS, DSS, and DFS. While respecting the limitations of retrospective cohort studies, overall outcomes in this cohort are inferior to those predicted for TMT, but adherence to best practices such as maximal TURBT and combined modality chemoRT result in acceptable long term survival rates.

e16596 Background: Contemporary real-world data on treatment practices for patients with localized bladder cancer is limited. In this study we examined treatment patterns for patients diagnosed with de novo MIBC in Alberta. In addition, we evaluated the impact of patient demographics on treatment selection. Methods: We conducted a retrospective, observational cohort study of patients diagnosed with de novo MIBC between 2010-2022 using population-level administrative databases. Data sources included Alberta Cancer Registry, Vital Statistics, Pharmaceutical Information Network, Health Practitioner Claims, Discharge Abstract Database and National Ambulatory Care Report System databases. De novo MIBC was defined as initial presentation of UC with stage T2-T4, N0-N3, and M0 urothelial bladder cancer. Patients were followed from diagnosis to last known contact with the healthcare system, end of 2021, or death. Treatment patterns were descriptively summarized with stratified analyses performed according to treatment. Kaplan-Meier technique was used to estimate median overall survival (OS). Results: Overall, 1,292 de novo MIBC patients were identified: 76% male, mean age of 73 years. Overall, 50.3% of underwent a radical cystectomy (RC), 9% received chemoradiotherapy, 3.6% chemotherapy only, 12% radiation only, and 25% did not receive active treatment. Of those receiving RC (n=651), 51% received perioperative chemotherapy. Overall, 43.5% of the cohort received neoadjuvant systemic therapy with 12.6% receiving adjuvant systemic therapy. Stratification by treatment revealed most patients receiving radiation or no treatment were >75 years (86% and 73%, respectively) with a Charlson comorbidity index (CCI) ≥1 (64% and 67% respectively). The majority of patients receiving RC or chemoradiotherapy were ≤75 year (77% and 63%) with a CCI=0 (61% and 53%).Median OS was 26 months from MIBC diagnosis and differed by treatment group: 83.3 months for RC with perioperative chemo, 42.4 months for RC w/o chemotherapy, 24.8 months for chemotherapy + radiation, 16.2 months for chemotherapy alone, 8.6 months for no therapy and 7 months for radiation alone. Conclusions: This real-world cohort of de novo MIBC demonstrates a significant use of definitive surgical care (50%) compared to chemoradiotherapy (9%) with over one third of patients not receiving curative intent treatment. Notably, 40% of patients received neoadjuvant systemic therapy, aligning to current guideline recommended treatment strategies. Variations in care were found as treatment modalities differed considerably based on patient characteristics. While this likely reflects appropriate clinical care, selection biases limit accurate conclusions regarding efficacy. These data highlight the need to better understand drivers for treatment selection in MIBC given potential influence on outcomes.

Supplementary Figure S2. PFS, 1.00 mg/kg vs Total Study Population and CPIExposed Population (Parts A, B, and C, FAS)

Abstract Fibroblast growth factor receptor (FGFR) gene alterations are common in urothelial cancer (UC) and targetable with erdafitinib. The co-approved companion diagnostic is an amplicon-based tumor tissue test that detects a limited number of recurrent FGFR alterations. However, FGFR status may change during disease progression, and rare FGFR alterations not typically covered by existing tests may be of clinical importance. Therefore, in a prospective pan-Canadian study (NCT06129084), we compared standard archival tissue testing to broad targeted sequencing of cell-free circulating tumor DNA (ctDNA) to detect FGFR alterations in UC. Eligible patients had progressing metastatic UC and were undergoing tissue FGFR testing. Blood was drawn at study enrollment and plasma cell-free DNA and matched white blood cell DNA underwent deep-targeted sequencing with a hybridization capture panel including the introns and exons of FGFR1-4 and the common breakpoint region of TACC3. Archival tissue selection and testing was initiated by the treating physician and typically used the Oncomine Focus assay. 210 patients were enrolled across 12 sites, and 140 patients have tissue and ctDNA results available for concordance assessment. 43/140 (31%) of cell-free DNA samples had low tumor fraction (<0.5%) and were considered inconclusive. For the remaining 97 same-patient tissue and ctDNA pairs, FGFR status was identical in 88 (91%). In 7 of 9 discordant cases, the tissue was negative, but ctDNA was positive for FGFR alterations: these were enriched for FGFR3-TACC3 fusions (4/7). Two discordant fusions had canonical breakpoints that can be identified by current amplicon-based companion diagnostics, indicating potential spatiotemporal heterogeneity in somatic FGFR status. The other two discordant (ctDNA-only) fusions had non-canonical breakpoints that are not amenable to detection by current amplicon-based companion diagnostics. In two mutation discordant cases (S249C positive in ctDNA only), lack of signal in tumor tissue could be explained by the presence of additional FGFR3 variants within 25bp of S249 and in cis - disrupting primer binding sites. There were only two cases of tissue-only FGFR alterations among the 97 evaluable pairs (FGFR3-TACC3 fusion, S249C). ctDNA testing of metastatic UC with a broad capture-based approach covering all exons and introns of FGFR genes can identify additional alterations not detected with current amplicon-based companion diagnostics applied to archival tissue. Our results support ctDNA testing as a valuable adjunct to tissue testing, but not as a replacement due to the high frequency of inconclusive ctDNA results, secondary to tumor fraction below the threshold. Assay design, including target enrichment technique, is a significant source of variability in tissue and ctDNA FGFR status and should be carefully considered in future clinical biomarker testing strategies. Citation Format: David C. Müller, Gillian Vandekerkhove, Andrew J. Murtha, Jack V.W. Bacon, Carlos Vasquez-Rios, Maria Stephenson, Kimia Rostin, Elena Schönlau, Connor Wells, Sunil Parimi, Krista Noonan, Naveen S. Basappa, Jenny J. Ko, Daygen Finch, Nimira Alimohamed, Tarek A. Bismar, Gang Wang, Andreas Papadakis, Lucia Nappi, Matti Annala, Cecily Q. Bernales, Alan Spatz, Kim N. Chi, Alexander W. Wyatt, Bernhard J. Eigl. Clinical test design affects tumor tissue and ctDNA FGFR gene status in metastatic urothelial cancer: a prospective study [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr A004.

Supplementary Table S4. TEAEs (≥10% Patients) by SOC and PT: Part A, Escalation Phase

Supplementary Figure S1. Patient Disposition.