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

Background: 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.

Methods: 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/m² 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/m² 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 populations. The ITT population for this analysis comprised concurrently enrolled patients in groups B and C who were randomly assigned to treatment. For the safety analysis, all patients enrolled in group B and group C who received any study treatment were included. The trial is registered with ClinicalTrials.gov, NCT02807636, and is active but no longer recruiting.

Findings: Between July 15, 2016, and July 20, 2018, 1213 patients were enrolled and randomly assigned to treatment, of whom 362 patients were assigned to group B and 400 to group C, of whom 360 and 359, respectively, were enrolled concurrently (ITT population). 543 (76%) of 719 patients were male, 176 (24%) were female, and 534 (74%) were White. As of data cutoff (Aug 31, 2022), after a median follow-up of 13·4 months (IQR 6·2-30·8), median overall survival was 15·2 months (95% CI 13·1-17·7; 271 deaths) in group B and 13·3 months (11·9-15·6; 275 deaths) in group C (stratified hazard ratio 0·98 [95% CI 0·82-1·16]). The most common grade 3-4 treatment-related adverse events were anaemia (two [1%] in patients who received atezolizumab monotherapy vs 133 [34%] in those who received placebo plus chemotherapy), neutropenia (one [<1%] vs 115 [30%]), decreased neutrophil count (0 vs 95 [24%]), and decreased platelet count (one [<1%] vs 92 [24%]). Serious adverse events occurred in 163 (46%) patients versus 196 (50%). Treatment-related deaths occurred in three (1%; n=1 each, pneumonia, interstitial lung disease, large intestinal obstruction) patients who received atezolizumab monotherapy and four (1%; n=1 each, diarrhoea, febrile neutropenia, unexplained death, toxic hepatitis) who received placebo plus chemotherapy.

Interpretation: The final analysis from IMvigor130 did not show a significant improvement in overall survival with first-line atezolizumab monotherapy compared with platinum-based chemotherapy in the intention-to-treat population. The safety profile of atezolizumab monotherapy remained acceptable after extended follow-up, with no new safety signals.

Funding: F Hoffmann-La Roche.