Clinical Outcomes of Sacituzumab Govitecan (SG) after Prior Exposure to Enfortumab Vedotin (EV) in Patients with Metastatic Urothelial Carcinoma (Muc).

4581 Background: SG is a TROP-2 directed antibody-drug conjugate (ADC) approved as advanced-line treatment for mUC after platinum-based chemotherapy and a checkpoint inhibitor, based on phase II study (TROPHY-U-01) that demonstrated objective response rate (ORR) of 28%, median progression free survival (PFS) of 5.4 months (mo) and median overall survival (OS) of 10.9 mo. Current guidelines for mUC endorse using SG in post EV setting, more so with the recent FDA approval of EV and pembrolizumab as the new standard of care for 1st line. Data is scarce regarding the efficacy of SG in patients previously treated with EV, as only 10 patients (8.8%) included in TROPHY-U-01 cohort 1 had prior EV exposure. Here, we report real-world clinical outcomes for SG post EV. Methods: This is a single center retrospective cohort of patients with mUC treated with SG after prior exposure to EV. Demographics and clinical data were collected retrospectively by chart review. Clinical response to SG and EV was defined by physician assessment. Cases with objective response to SG per clinical review [complete response (CR) + partial response (PR)] were then confirmed by formal radiological evaluation using RECIST 1.1. PFS and OS defined from start of SG were calculated using the Kaplan-Meier method. Results: 82 patients were identified, median age was 71 years (range 47-83), 70% male and 37% upper tract primary. Lung, bone, liver and brain metastases were present in 67%, 62%, 50% and 13% of patients, respectively. Median prior treatment lines were 3 (range 1-8), 68% of patients received SG directly post EV. Most patients were treated with single agent EV, though 8 patients (10%) received combination of EV + pembrolizumab. PR was confirmed in 8 patients, and none had CR, resulting in an ORR of 10% (95% CI 4.3%, 18.3%). Stable disease (SD) was achieved in 16 patients (20%, 95% CI 11.9%, 30.4%) amounting to disease control rate (DCR = CR+PR+SD) of 30% (95% CI 20.3%, 41.3%). Median PFS was 2.1 mo (95% CI 1.9, 2.5) and median OS was 6.0 mo (95% CI 4.5, 7.0). There was no association between response to EV and ORR, PFS or OS after SG (p>0.8). Sequencing SG directly after EV was associated with improved ORR (p = 0.028) and PFS (HR=0.43, 95% CI 0.21, 0.87, p=0.02, adjusted for tumor location, treatment line and liver metastasis) but not OS. Dose reductions were required upfront in 18%, on treatment in 44% or both in 7%. Prophylactic granulocyte stimulating factor (GCSF) was used in 57 patients (70%), rates of G3-4 neutropenia, anemia and thrombocytopenia were 36%, 36% and 4% respectively. Conclusions: In our large cohort of real-world advanced mUC patients with prior exposure to EV, SG resulted in limited clinical efficacy compared to previous reports. There was an association between SG administration directly after EV and improved clinical outcomes. Further investigations are warranted to explore optimal treatment sequencing.