Prognostic and Treatment-Context Associations of EASIX and IPI in Extensive-Stage Small-Cell Lung Cancer Patients Receiving First-Line Therapy

Background: The comparative prognostic value of the Endothelial Activation and Stress Index (EASIX) and the Inflammatory Prognostic Index (IPI) in extensive-stage small-cell lung cancer remains unclear. This study aimed to compare the prognostic value of EASIX and IPI and assess their contribution beyond established clinical factors. Methods: This retrospective single-center study included 129 patients with de novo extensive-stage small-cell lung cancer who initiated first-line systemic therapy between December 2022 and October 2025. Pretreatment EASIX and IPI values were analyzed as log2-transformed continuous variables in multivariable Cox models. Overall survival was the primary outcome, and first-line progression-free survival was the secondary outcome. Results: During a median follow-up of 26.91 months, 116 deaths and 123 progression-or-death events occurred. Each doubling of the EASIX value was independently associated with a higher hazard of death (adjusted hazard ratio, 1.14; 95% confidence interval, 1.01–1.28; p = 0.019), whereas IPI was not independently associated with overall survival. Neither index was independently associated with first-line progression-free survival. Adding EASIX to the clinical model improved model fit and increased the C-index from 0.619 to 0.650, whereas IPI provided no additional prognostic contribution. Conclusions: EASIX may provide prognostic information beyond established clinical factors for overall survival in extensive-stage small-cell lung cancer. These findings warrant validation in larger multicenter cohorts.