Subgroup Analysis of Japanese Patients in a Phase I/III Study of Atezolizumab in ES-SCLC (IMpower133)

Abstract

Background: Atezolizumab, an anti-programmed death-ligand 1 (PD-L1) agent, is effective and well tolerated in the first-line treatment of Extensive-Stage Small Cell Lung Cancer (ES-SCLC). We assessed its efficacy and safety in Japanese patients through subgroup analyses of the phase 3 IMpower133 trial (NCT02763579). Methods: IMpower133 is a Phase I/III, multicenter, double-blinded, placebo-controlled randomized trial evaluating atezolizumab plus carboplatin and etoposide in chemotherapy-naïve ES-SCLC patients. Patients were randomly assigned in a 1:1 ratio to receive carboplatin and etoposide with either atezolizumab or placebo for four 21- day cycles (induction phase), followed by a maintenance phase during which they received either atezolizumab or placebo until they had unacceptable toxicity, disease progression according to Response Evaluation Criteria in Solid Tumors, version 1.1, or no additional clinical benefit. The two primary endpoints were investigator-assessed progression-free survival and overall survival in the intention-to-treat population. Results: Of the 403 patients randomized in the IMpower133 trial, 42 patients were enrolled from Japanese centers. In Japanese patients from the ITT population, median PFS in the atezolizumab group (n=20) was longer than the placebo group (n=22; 4.5 months [95% CI, 4.2-8.1] vs 4.0 months [95% CI, 2.9-5.6], respectively; HR 0.47 [95% CI, 0.23-0.96]), and median OS in the atezolizumab group was longer than the placebo group (14.6 months [95% CI, 11.8-17.8] vs 11.9 months [95% CI, 8.4-15.8], respectively; HR 0.72 [95% CI, 0.31-1.67]). The atezolizumab regimen was generally well tolerated, with no treatment-related deaths. Conclusion: The addition of atezolizumab to carboplatin and etoposide was effective and well tolerated in Japanese patients with ES-SCLC. Results are consistent with the primary analysis of IMpower133 trial.