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LBA443 Background: The 2 primary endpoints of the CheckMate 274 trial were met as nivolumab (NIVO) improved disease-free survival (DFS) versus placebo (PBO) in the intent-to-treat (ITT) population and in patients with tumor programmed death ligand 1 (PD-L1) expression ≥ 1%. We report extended follow-up data. Methods: CheckMate 274 is a phase 3, double-blind trial of adjuvant NIVO versus PBO for high-risk muscle-invasive urothelial carcinoma (MIUC) (bladder, ureter, or renal pelvis) after radical resection. Patients were randomly assigned 1:1 to NIVO 240 mg every 2 wk or PBO for ≤ 1 year of treatment. Patients had pathologic evidence of UC at high risk of recurrence and Eastern Cooperative Oncology Group performance status (ECOG PS) ≤ 1. Primary endpoints were DFS in ITT patients and in patients with PD-L1 ≥ 1%. DFS was also analyzed in prespecified subgroups. Overall survival and non–urothelial tract recurrence-free survival (NUTRFS) in ITT patients and in patients with PD-L1 ≥ 1% were secondary endpoints. Distant metastasis-free survival (DMFS) and safety were exploratory endpoints. Results: There were 353 patients randomly assigned to NIVO (PD-L1 ≥ 1%, n = 140) and 356 to PBO (PD-L1 ≥ 1%, n = 142). With median follow-up of 36.1 months (minimum follow-up, 31.6 months), median DFS was 22.0 months with NIVO versus 10.9 months with PBO in ITT patients and 52.6 months with NIVO versus 8.4 months with PBO in patients with PD-L1 ≥ 1% (Table). DFS benefit was seen in most subgroups analyzed including age, sex, ECOG PS, nodal status, prior cisplatin-based chemotherapy, and PD-L1 status. NUTRFS and DMFS benefits with NIVO versus PBO were also observed in both populations (Table). Grade 3–4 treatment-related adverse events occurred in 18.2% and 7.2% of patients in the NIVO and PBO arms, consistent with the primary analysis. Overall survival will be assessed at a future database lock. Conclusions: With extended follow-up, NIVO continued to show DFS, NUTRFS, and DMFS benefits versus PBO. The hazard ratio (HR) for DFS and NUTRFS in PD-L1 ≥ 1% patients and for DMFS in both ITT and PD-L1 ≥ 1% patients also continued to improve versus the primary analysis. No new safety signals were identified. These results further support adjuvant NIVO as a standard of care for high-risk MIUC after radical resection. Clinical trial information: NCT02632409 . [Table: see text]

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