Atezolizumab monotherapy versus chemotherapy in untreated locally advanced or metastatic urothelial carcinoma (IMvigor130): final overall survival analysis from a randomised, controlled, phase 3 study

The primary analysis of IMvigor130 showed a significant progression-free survival benefit with first-line atezolizumab plus platinum-based chemotherapy (group A) versus placebo plus platinum-based chemotherapy (group C) in patients with locally advanced or metastatic urothelial cancer. However, this finding did not translate into significant overall survival benefit for group A versus group C at the final analysis, precluding formal statistical testing of outcomes with atezolizumab monotherapy (group B) versus group C. Here we report the final overall survival results for group B versus group C; this report is descriptive and should be considered exploratory due to the study's statistical design. In this global, partially blinded, randomised, controlled, phase 3 study, patients (aged ≥18 years) who had locally advanced or metastatic urothelial cancer previously untreated in the metastatic setting and Eastern Cooperative Oncology Group performance status of 0-2 were enrolled at 221 hospitals and oncology centres in 35 countries. Patients were randomly assigned (1:1:1), using a permuted block method (block size of six) and an interactive voice and web response system, stratified by PD-L1 status, Bajorin score, and investigator's choice of platinum-based chemotherapy, to receive either atezolizumab plus platinum-based chemotherapy (group A), atezolizumab alone (group B), or placebo plus platinum-based chemotherapy (group C). Sponsors, investigators, and patients were masked to assignment to atezolizumab or placebo in group A and group C; atezolizumab monotherapy in group B was open label. For groups B and C, atezolizumab (1200 mg) or placebo was administered intravenously every 3 weeks. Chemotherapy involved 21-day cycles of gemcitabine (1000 mg/m body surface area on day 1 and day 8 of each cycle) plus the investigator's choice of carboplatin (area under the curve 4·5 mg/mL per min or 5 mg/mL per min) or cisplatin (70 mg/m body surface area), administered intravenously. Co-primary endpoints were progression-free survival and overall survival in group A versus group C, and overall survival in group B versus group C, tested hierarchically, in the intention-to-treat (ITT) population, and then the populations with high PD-L1 tumour expression (immune cell [IC] expression score of IC2/3) if the results from group A versus group C were significant. Here, we report the co-primary endpoint of overall survival for group B versus group C in the ITT and IC2/3 populatio