Early Tumor Shrinkage as a Predictor of Favorable Treatment Outcomes in Patients With Extensive- Stage SCLC Who Received Programmed Cell Death- Ligand 1 Inhibitor Plus Platinum-Etoposide Chemotherapy: A Prospective Observational Study

Introduction: In recent years, programmed cell death-ligand 1 (PD-L1) inhibitor plus platinum-etoposide chemo-therapy was found to have favorable clinical outcomes in patients with extensive-stage SCLC (ES-SCLC). The useful-ness of early tumor shrinkage (ETS) has been reported in various types of cancers. Nevertheless, there have been few reports evaluating ETS in ES-SCLC. Therefore, this study aimed to evaluate the role of ETS in the clinical outcomes of patients with ES-SCLC receiving chemoimmunotherapy. Methods: We prospectively identified 46 patients with ES-SCLC who received PD-L1 inhibitor plus platinum-etoposide chemotherapy at 10 institutions in Japan between September 2019 and October 2021. Of them, 35 patients were selected for analyses. Results: The responders (progression-free survival [PFS] >= 6.0 mo) had significantly greater tumor shrinkage at the first evaluation than the nonresponders (PFS < 6.0 mo) (65.0% versus 53.7%, p = 0.03). We defined the cutoff value for ETS as a 57% change from the baseline on the basis of the receiver operating characteristic results to determine the optimal tumor shrinkage rate at the first evaluation for identifying responders. The patients with ES-SCLC who ach-ieved ETS had longer PFS and overall survival than those who did not achieve ETS (5.6 versus 4.0 mo, log-rank test p = 0.001 and 15.0 versus 8.3 mo, log-rank test p = 0.02). In the multivariate analyses, ETS was significantly associated with PFS and overall survival (hazard ratio = 0.27, 95% confi-dence interval: 0.12-0.63, p = 0.002 and hazard ratio = 0.34, 95% confidence interval: 0.13-0.85, p = 0.02). Conclusions: Our prospective observational study indi-cated that ETS was related to favorable clinical outcomes for patients with ES-SCLC receiving PD-L1 inhibitor plus platinum-etoposide chemotherapy. (c) 2023 The Authors. Published by Elsevier Inc. on behalf of the International Association for the Study of Lung Cancer. This is an open access article under the CC BY-NC-ND li-cense (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).