Subgroup Analysis of Japanese Patients in a Phase III Study of Atezolizumab in Extensive-stage Small-cell Lung Cancer (IMpower133)

Atezolizumab is effective and well-tolerated in patients with extensive-stage small-cell lung cancer (ES-SCLC), but differences in response to systemic therapy exist between Asian and Caucasian patients. Here, we assess the efficacy and tolerability of atezolizumab in Japanese patients from the IMpower133 trial (NCT02763579).Key eligibility criteria for this multicenter, double-blind, placebo-controlled, randomized study included age ≥ 18 years; histologically or cytologically confirmed ES-SCLC, measurable per Response Evaluation Criteria in Solid Tumors version 1.1; an Eastern Cooperative Oncology Group performance status of 0/1; and no prior systemic treatment for ES-SCLC. Patients were treated with either atezolizumab 1200 mg or placebo with carboplatin (area under the curve of 5 mg/mL/min) and etoposide (100 mg/m2). Primary endpoints were overall survival and investigator-assessed progression-free survival in the intention-to-treat population. Of the 403 patients randomized in the IMpower133 trial, 42 were enrolled at Japanese centers.In Japanese patients in the intention-to-treat population, the median overall survival in the atezolizumab group (n = 20) was longer than that in the placebo group (n = 22; 14.6 months; 95% confidence interval [CI], 11.8-17.8 months vs. 11.9 months; 95% CI, 8.4-15.8, respectively; hazard ratio, 0.72; 95% CI, 0.31-1.67). The median progression-free survival was 4.5 months (95% CI, 4.2-8.1 months) versus 4.0 months (95% CI, 2.9-5.6 months; hazard ratio, 0.47; 95% CI, 0.23-0.96), respectively. Atezolizumab was generally well-tolerated, with no treatment-related deaths.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 the IMpower133 trial.