Efficacy of sacituzumab govitecan (SG) in locally advanced (LA) or metastatic urothelial cancer (mUC) by trophoblast cell surface antigen 2 (Trop-2) expression.

4579 Background: Patients (pts) with mUC have an estimated 5-year overall survival (OS) rate of 14%. Trop-2 is a transmembrane glycoprotein with elevated expression in many cancers, including UC. SG is a Trop-2–directed antibody-drug conjugate with accelerated FDA approval for pts with LA unresectable or mUC who previously received platinum (PT) and a checkpoint inhibitor (CPI). SG has demonstrated activity in 3 phase 2 TROPHY-U-01 mUC cohorts: Cohort 1 (C1), 28% objective response rate (ORR); Cohort 2 (C2), 32% ORR; and Cohort 3 (C3), 41% ORR. Here, we assess efficacy outcomes in C1-3 by Trop-2 archival tumor expression. Methods: Pts (≥18 years) with previously treated (PT [C3], CPI [C2], or both [C1]) LA or mUC received SG (10 mg/kg IV) on D1 and D8 of 21-D cycles; C3 pts also received pembrolizumab (200 mg) on D1 of 21-D cycles. The primary endpoint was ORR by independent review. Archival tumor samples collected at enrollment were assessed for Trop-2 protein expression using SP295 anti–Trop-2 antibody by IHC with assessment by histological scores (H-scores; scale, 0-300) and % of membrane-positive tumor cells (Roche Tissue Services). Trop-2 association with clinical endpoints was evaluated using unstratified Cox proportional hazards models for survival data and logistic regression for ORR. Results: At data cutoff, 192 pts were enrolled in C1-3; 144 pts (75%) had samples evaluable for Trop-2 prevalence and 139 pts (72%) were evaluable for efficacy analysis by Trop-2 expression (5 pts not assigned to any cohort were excluded). Baseline characteristics for pts with evaluable samples were consistent with the overall population. Median (IQR) Trop-2 H-score and % of membrane-positive tumor cells for evaluable pt samples were 215 (180-247) and 92% (75-98), respectively; these readouts were highly correlated (ρ=0.82, P<0.001). ORRs for C1 samples with below (n=42) and above (n=45) median Trop-2 H-scores were 24% and 29% ( P=0.59), respectively; median progression-free survival (PFS) was 3.4 and 6.7 months (HR=0.765, P=0.262), respectively; and median OS was 9.9 and 10.9 months (HR=0.978, P=0.927), respectively. Median PFS for C1 samples with below and above median Trop-2 membrane positivity were 3.9 and 6.2 months (HR=0.835, P=0.443), respectively. Analyses of efficacy endpoints for C2 and C3 pt samples by Trop-2 expression were consistent with C1 results. Conclusions: In this analysis of archival tumor samples from pts with pretreated LA or mUC, Trop-2 protein was highly expressed across cohorts, supporting prior Trop-2 expression analyses in UC. Similar outcomes were observed between C1 pts with samples that were below and above median Trop-2 H-score with most pronounced numerical differences observed for PFS. These results suggest that SG activity may be independent of Trop-2 expression in UC, but additional studies are needed to confirm these results. Clinical trial information: NCT03547973 .