Baseline Gustave Roussy Immune Score and Survival in Extensive-Stage Small-Cell Lung Cancer Treated with First-Line Chemoimmunotherapy

Background: First-line chemoimmunotherapy has improved outcomes in extensive-stage small-cell lung cancer (ES-SCLC), but survival remains heterogeneous and routine-care prognostic tools are limited. Patients and Methods: We retrospectively analyzed consecutive adults with stage IV ES-SCLC treated with platinum-etoposide plus a programmed death-ligand 1 inhibitor at three Spanish hospitals from August 2021 to December 2024. Outcomes included overall survival (OS), progression-free survival (PFS), objective response, and immune-related toxicity. Baseline Gustave Roussy Immune Score (GRIm) was defined as high-risk when at least two of albumin < 35 g/L, lactate dehydrogenase above the upper limit of normal, and neutrophil-to-lymphocyte ratio > 6 were present. Baseline Cox models included high-risk GRIm, platelet-to-lymphocyte ratio > 180, and Eastern Cooperative Oncology Group performance status ≥ 2; maintenance exposure was assessed in a 3-month OS landmark analysis. Analyses were exploratory. Results: Among 51 patients, mean age was 64.2 years, 72.5% were men, and 82.3% had ECOG performance status 0– 1. During follow-up, 43 deaths and 50 PFS events occurred. Objective response rate was 70.6%, median OS was 11.9 months, and median PFS was 5.7 months. Median OS was 14.2 months with low-risk GRIm and 5.4 months with high-risk GRIm. High-risk GRIm was independently associated with worse OS (hazard ratio [HR] 5.59) and PFS (HR 3.50), while PLR > 180 was associated with worse OS (HR 2.37). In the 3-month landmark cohort (n=47), maintenance exposure remained associated with longer OS (HR 0.21), although this analysis remained vulnerable to residual selection bias. Conclusion: Baseline GRIm was the most consistent candidate prognostic marker in this real-world ES-SCLC cohort. The study did not assess prediction of immunotherapy benefit, and prospective validation is warranted before treatment decisions are guided by GRIm. Keywords: small-cell lung cancer, chemoimmunotherapy, maintenance, GRIm, prognostic biomarkers, real-world evidence