Atezolizumab monotherapy for metastatic urothelial carcinoma: final analysis from the phase II IMvigor210 trial

Background: The IMvigor210 trial demonstrated clinical benefit and manageable toxicity with atezolizumab monotherapy [anti-programmed death-ligand 1 (PD-L1)] in patients with metastatic urothelial carcinoma (UC) in primary analyses. Final efficacy and safety results after long-term follow-up are reported.

Patients and methods: This phase II single-arm trial of atezolizumab monotherapy in patients with advanced UC included two cohorts: untreated patients ineligible for cisplatin-based chemotherapy (cohort 1; n = 119) and those previously treated with platinum-based chemotherapy (cohort 2; n = 310). Atezolizumab was administered i.v. (1200 mg every 21 days) until progression or unacceptable toxicity. Primary endpoints were independent review facility-assessed confirmed objective response rate (ORR) per RECIST 1.1 in cohort 1 and independent review facility-assessed ORR per RECIST 1.1 and investigator-assessed modified (m)RECIST in cohort 2. Overall survival (OS), efficacy by PD-L1 status, and safety were also assessed.

Results: At data cut-off (1 June 2023), the median survival follow-up was 96.4 months (range, 0.2-103.4 months) in cohort 1 and 46.2 months [0.2 (censored)-54.9 months] in cohort 2. In cohort 1, the ORR [95% confidence interval (CI)] was 23.5% (16.2% to 32.2%) in all patients and 28.1% (13.8% to 46.8%) in the PD-L1 tumor-infiltrating immune cell (IC)2/3 subgroup. Median OS (95% CI) was 16.3 months (10.4-24.5 months) overall and 12.3 months (6.0-49.8 months) in the PD-L1 IC2/3 subgroup. In cohort 2, the ORR (95% CI) was 16.5% (12.5% to 21.1%) per RECIST 1.1 and 19.7% (95% CI 15.4% to 24.6%) per mRECIST in all patients and 27.0% (18.6% to 36.8%) and 28.0% (19.5% to 37.9%), respectively, in the PD-L1 IC2/3 subgroup. Median OS (95% CI) was 7.9 months (6.7-9.3 months) in all patients and 11.9 months (9.0-22.8 months) in the IC2/3 subgroup. Treatment-related grade 3/4 adverse events occurred in 21.8% (cohort 1) and 18.7% (cohort 2); one treatment-related death occurred in cohort 1.

Conclusions: With long-term follow-up, atezolizumab monotherapy demonstrated clinically meaningful efficacy with durable responses in a subset of patients with metastatic UC; there were no new safety signals.