Kikuchi, Eiji

TPS890 Background: Although first-line (1L) EV + pembrolizumab has improved outcomes for patients with la/mUC, most experience disease progression, highlighting an unmet need for novel therapies. TROP2 is a glycoprotein highly expressed in several epithelial tumors, including UC. Dato-DXd is a TROP2-directed antibody–drug conjugate comprising an anti-TROP2 monoclonal antibody, a tetrapeptide-based cleavable linker, and a topoisomerase I inhibitor payload (DXd), designed to induce selective tumor-cell death and reduce systemic exposure to the payload. Dato-DXd has demonstrated durable efficacy and a manageable safety profile in patients with la/mUC both as monotherapy (TROPION-PanTumor01 [NCT03401385]) and in combination with immunotherapy (TROPION-PanTumor03 [NCT05489211]). We describe a phase 2/3 trial comparing the efficacy and safety of Dato-DXd + platinum CT (carboplatin or cisplatin) vs gemcitabine + platinum CT in participants with la/mUC with disease progression on or after EV + pembrolizumab. Methods: TROPION-Urothelial03 (NCT07129993) is a global, multicenter, randomized, open-label, phase 2/3 trial. In part A (phase 2), ~60 participants will be randomized 1:1 to receive Dato-DXd 4 or 6 mg/kg + platinum CT. In part B (phase 3), ~570 participants will be randomized 1:1 to receive Dato-DXd at the recommended phase 3 dose (determined using part A data) + platinum CT vs gemcitabine + platinum CT. Randomization in part A is stratified by assignment of platinum CT (carboplatin vs cisplatin), and in part B, by assignment of platinum CT, presence vs absence of liver metastasis at screening, and time to progression on 1L EV + pembrolizumab ( < 6 vs ≥6 months). Study treatment continues until disease progression, unacceptable toxicity, withdrawal of consent, death, loss to follow-up, or other reasons per protocol. Radiographic tumor assessments occur every 6 weeks for 54 weeks, then every 12 weeks. The primary endpoint of part A is objective response rate (ORR) by investigator per Response Evaluation Criteria in Solid Tumours, version 1.1 (RECIST 1.1). The dual primary endpoints of part B are progression-free survival (PFS) by blinded independent central review (BICR) per RECIST 1.1 and overall survival (OS). Secondary endpoints include duration of response by investigator per RECIST 1.1 (part A), and PFS by investigator per RECIST 1.1 and ORR by BICR and investigator per RECIST 1.1 (part B). In part A, ORR will be summarized with 2-sided 95% exact confidence intervals using the Clopper–Pearson method by trial group. In part B, PFS and OS will be compared between trial groups using a log-rank test stratified by randomization stratification factors, with hazard ratios from the stratified Cox regression model. Clinical trial information: NCT07129993 .

475 Background: Emerging evidence supports use of neoadjuvant chemotherapy (NAC) prior to radical nephroureterectomy (RNU) for appropriately selected patients with upper tract urothelial carcinoma (UTUC). However, oncologic outcomes have not been well characterized for patients with residual muscle-invasive disease after NAC. Methods: We used a multi-institutional cohort from 24 centers in the U.S., Europe, and Japan to retrospectively identify patients who underwent RNU for UTUC from 1985-2022 and had high-grade muscle-invasive disease. We stratified the cohort based on receipt of NAC (>ypT2 vs. >pT2). Exclusion criteria included receipt of adjuvant chemotherapy, concurrent cystectomy with RNU, and distant metastatic disease. Baseline characteristics were compared between groups. Kaplan-Meier survival analysis with log-rank test was used to compare differences in recurrence-free survival (RFS), overall survival (OS), and cancer-specific survival (CSS). Multivariable Cox regression and Fine-Gray competing risk regression were used to determine predictors of these outcomes. Results: A total of 1,233 patients were included, 62 of whom received NAC prior to RNU. A platinum-based regimen was used in 90% of NAC recipients, and the median number of cycles administered was 4 (IQR: 3-5). Median follow-up time among all patients was 22 months (IQR: 8-47 mo.). NAC recipients were more likely to have pathologic node positivity (35% vs. 13%) and less likely to have positive tumor margins (8% vs. 28%). On Kaplan-Meier analysis, NAC recipients with residual >ypT2 disease had poorer outcomes than those with >pT2 disease (2-year RFS [NAC vs. no NAC]: 52% vs. 80%, p<0.001; 2-year OS: 60% vs. 78%, p=0.003; 2-year CSS: 61% vs. 86%, p<0.001). Multivariable analyses also showed a statistically significant association between residual muscle-invasive disease after NAC and poorer RFS, OS, and CSS (Table). Conclusions: NAC recipients with >ypT2 disease at RNU after exhibit poorer outcomes than stage-matched chemotherapy naïve counterparts. This may reflect effects of occult micrometastatic disease or chemoresistant primary tumors in non-responders. Our data highlight the need to improve prospective identification of candidates most likely to respond to NAC prior to RNU for UTUC in order to maximize its therapeutic benefit. [Table: see text]