Background: Two interim OS analyses from IMvigor130 demonstrated non-statistically significant OS benefit with atezo monotherapy (Arm B) vs placebo + platinum (investigator [INV] choice of carboplatin or cisplatin [carbo or cis])/gemcitabine (plt/gem; Arm C) in patients (pts) with PD-L1–high (IC2/3) mUC, as well as a favorable safety profile vs chemo (Galsky Lancet 2020, Davis AACR 2021). Exploratory data showed clinical benefit with atezo monotherapy in cis-ineligible pts with IC2/3 tumors. Here, we report the final OS analysis from IMvigor130 Arms B and C. Methods: Pts were randomly assigned 1:1:1 to Arm A (atezo + plt/gem; not reported here), B or C. Due to the statistical testing hierarchy, no formal comparison of OS (co-primary endpoint) in Arm B vs C was performed in ITT and IC2/3 pts. ORR and DOR, both per INV-assessed RECIST 1.1 (secondary endpoints), and safety were assessed. Subgroup analyses of OS in cis-ineligible pts and disease control rate (DCR, confirmed CR, PR or [SD ≥6 mo]) were exploratory. Results: As of data cutoff Aug 31, 2022, time since last pt randomly assigned was 49 mo. OS data (Table) did not show benefit for ITT pts, while an HR of 0.56 (0.34, 0.91) was seen in the cis-ineligible IC2/3 subgroup. In the ITT population, the 24-mo OS rates were 34% in Arm B and 32% in Arm C. ORR was 24% (87/359; 38% DCR) in Arm B and 44% (158/356; 59% DCR) in Arm C; median DOR was 29.6 and 8.1 mo, respectively. In cis-ineligible IC2/3 pts, ORR was 40% (20/50) in Arm B and 33% (14/43) in Arm C. Median DOR was not evaluable in Arm B and 6.2 mo in Arm C. Of safety-evaluable pts, 57 of 354 in Arm B (16%) and 312 of 389 in Arm C (80%) had a Gr 3/4 treatment-related AE (TRAE); 3 (1%) and 4 (1%), respectively, had a Gr 5 TRAE. Gr 3/4 AEs of special interest occurred in 36 pts (10%) in Arm B and 17 (4%) in Arm C. Conclusions: The final OS analysis was consistent with previous data. Atezo monotherapy continued to show better tolerability vs chemo with no new safety concerns. These exploratory data support the benefit-risk ratio of atezo monotherapy vs chemo for first-line cis-ineligible IC2/3 mUC. Clinical trial information: NCT02807636.

PD-L1 IC2/3: PD-L1–expressing immune cells on ≥5% of the tumor area (VENTANA SP142); IC0/1: <5%. ^aStratified by IC status, Bajorin risk score, INV choice of cis vs carbo. ^b Stratified by Bajorin risk score, INV choice of cis vs carbo.