A Randomized Non-Comparative Phase II Study of Anti-Programmed Cell Death-Ligand 1 Atezolizumab or Chemotherapy As Second-Line Therapy in Patients With Small Cell Lung Cancer: Results From the IFCT-1603 Trial

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 = 49; chemotherapy n = 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 = 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 : 0.84, 95% CI: 0.45-1.58; p = 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.