Comparative Effectiveness of Non-cisplatin First-line Therapies for Metastatic Urothelial Carcinoma: Phase 2 IMvigor210 Study Versus US Patients Treated in the Veterans Health Administration.

Background: First-line treatments for cisplatin-ineligible patients with metastatic urothelial carcinoma (mUC) include carboplatin-based chemotherapy and checkpoint inhibitors such as atezolizumab (anti-PD-L1).

Objective: To compare overall survival (OS) among patients with mUC treated in the first-line setting with atezolizumab versus carboplatin-based chemotherapies (any carboplatin-based regimens or carboplatin-gemcitabine).

Design, Setting, And Participants: Cisplatin-ineligible patients with mUC from the phase 2 trial IMvigor210 (ClinicalTrials.gov NCT02951767) treated with atezolizumab and patients from the Veterans Health Administration (VHA) health care system (2006-2017, with IMvigor210 eligibility criteria applied using proxy measurements) treated according to normal clinical practice.

Interventions: IMvigor210 cohort 1 patients were treated with atezolizumab, and real-world VHA cohorts were treated with carboplatin-based regimens.

Outcome Measurements And Statistical Analysis: Entropy-balance weighting was applied to balance prespecified baseline patient characteristics. OS was analyzed using weighted Kaplan-Meier and Cox methods.

Results And Limitations: The median OS was 15.0 mo with atezolizumab (n = 110), 12.1 mo with any carboplatin-based chemotherapy (n = 282), and 8.7 mo with carboplatin-gemcitabine (n = 120). An OS benefit occurred with atezolizumab versus carboplatin-based regimens after 9 mo (hazard ratio [HR] 0.43; p = 0.004) and with atezolizumab versus carboplatin-gemcitabine after 5 mo (HR 0.52; p = 0.005). Study limitations include a predominantly male VHA cohort and ≤24-mo follow-up. Adjustment for confounding, a potential limitation of nonrandomized studies, was limited by the availability of clinical measurements in the VHA data, which allowed for replication of IMvigor210 exclusions in the VHA cohorts.

Conclusions: First-line atezolizumab for cisplatin-ineligible mUC may provide an OS benefit over carboplatin-based treatments after 5-9 mo, depending on the regimen.

Patient Summary: Many patients with metastatic urothelial carcinoma are ineligible for cisplatin-based chemotherapy. This study compared patients from a clinical trial receiving the immunotherapeutic agent atezolizumab with those in Veterans Health Administration clinical practice receiving carboplatin-based chemotherapy. Atezolizumab provided a survival benefit over chemotherapy after 5-9 mo.