Pretreatment eosinophilia as a biomarker for adverse outcomes in non-small cell lung cancer patients receiving immune checkpoint inhibitors: A systematic review and meta-analysis.

In recent years, immune checkpoint inhibitors (ICIs) have transformed the therapeutic landscape of non-small cell lung cancer (NSCLC), yet treatment response and adverse events vary widely among patients. In response, the identification of reliable pretreatment biomarkers has become a major goal for many clinicians to enhance prognostication and personalized care. As such, this systematic review and meta-analysis aimed to evaluate whether pretreatment eosinophilia is associated with adverse clinical outcomes in NSCLC patients receiving ICI therapy. Following PRISMA guidelines, a comprehensive literature search was conducted across online databases through February 2025. Eligible studies included observational designs reporting associations between baseline eosinophil levels and overall survival, progression-free survival, or immune-related adverse events (irAEs) in ICI-treated NSCLC patients. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using random-effects models for both unadjusted and adjusted data. Eleven studies met inclusion criteria. Pretreatment eosinophilia was associated with a nonsignificant reduction in overall survival based on both unadjusted analyses (OR: 0.79, 95% CI: 0.42-1.51 and OR: 0.74, 95% CI: 0.53-1.03, respectively). Similarly, a nonsignificant reduction in progression-free survival was found in unadjusted models (OR: 0.78, 95% CI: 0.54-1.13), whereas adjusted data revealed a significant negative association (OR: 0.68, 95% CI: 0.58-0.80). In contrast, eosinophilia was significantly associated with increased odds of irAEs in both unadjusted and adjusted analyses (OR: 3.19, 95% CI: 2.11-4.83 and OR: 3.35, 95% CI: 2.25-5.02, respectively). These findings indicate that pretreatment eosinophilia may serve as a useful prognostic biomarker indicating increased susceptibility to irAEs and potentially poorer survival outcomes in ICI-treated NSCLC patients.