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Introduction: This randomized phase II trial aimed at evaluating the engineered programmed cell death ligand 1 (PD-L1) antibody atezolizumab in SCLC progressing after first-line platinum-etoposide chemotherapy. Methods: Patients were randomized 2:1 to atezolizumab (1200 mg intravenously every 3 weeks) until progression or unacceptable toxicity, or conventional chemotherapy (up to 6 cycles of topotecan or re-induction of initial chemotherapy). Patients were not selected based on PD-L1 tissue expression. The primary endpoint was objective response rate at 6 weeks. A two-stage design with 2:1 randomization and O'Brien-Fleming stopping rules was used. The null hypothesis was rejected if more than 12 of 45 patients were responders. Results: Overall, 73 patients were randomized (atezolizumab n ¼ 49; chemotherapy n ¼ 24). At 6 weeks, 1 of 43 eligible atezolizumab patients achieved an objective response (2.3%, 95% confidence interval [CI]: 0.0-6.8), whereas 8 others had stable disease (20.9% disease control rate; 95% CI: 8.8-33.1). Among eligible chemotherapy patients (n ¼ 20), 10% achieved an objective response (65% disease control rate). Median progression-free survival was 1.4 months (95% CI: 1.2-1.5) with atezolizumab and 4.3 months (95% CI: 1.5-5.9) with chemotherapy. Overall survival did not significantly differ between groups. Median overall survival was 9.5 months versus 8.7 months for the atezolizumab and the chemotherapy group, respectively (adjusted hazard ratio atezolizumab : 0.84, 95% CI: 0.45-1.58; p ¼ 0.60). Two atezolizumab patients (4.2%) experienced grade 3 fatigue, and two others grade 1 dysthyroidism. Among 53 evaluable specimens, only 1 (2%) had positive immunohistochemical PD-L1 staining (SP142 clone). Conclusions: Atezolizumab monotherapy in relapsed SCLC failed to show significant efficacy. No unexpected safety concerns were observed.

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