Elevated proportion of eosinophils predicts immune-related adverse events and improved survival in patients with gastric cancer treated with nivolumab.

[BACKGROUND] Immune checkpoint inhibitors (ICIs) have improved treatment outcomes for gastric cancer. However, immune-related adverse events (irAEs) pose a major challenge. This study aimed to identify predictive factors for irAE occurrence in patients with advanced or recurrent gastric cancer treated with nivolumab.

[METHODS] We retrospectively analyzed information of 115 patients with advanced or recurrent gastric cancer treated with nivolumab monotherapy or in combination with chemotherapy. Patient characteristics and laboratory data, including complete blood counts, and clinical outcomes were analyzed. Optimal cutoffs for potential predictive factors were determined using ROC curve analysis.

[RESULTS] irAEs developed in 21 patients, with a median onset time of 124 days after treatment initiation. Patients with an eosinophil proportion ≥ 4% showed higher irAE rates compared to those with < 4%. Multivariate analysis identified eosinophil proportion ≥ 4% (odds ratio 5.0) and neutrophil-to-lymphocyte ratio < 1.9 (odds ratio 4.6) as independent predictors of irAE occurrence. Patients with an elevated eosinophil proportion had higher levels throughout the treatment than those without irAEs at baseline, two months, and three months after treatment initiation. Patients with eosinophil proportions ≥ 4% demonstrated better overall survival and a tendency toward improved progression-free survival.

[CONCLUSION] Elevated eosinophil proportion before ICI treatment was a predictor of irAE occurrence and was associated with improved survival in patients with advanced or recurrent gastric cancer. This readily available clinical parameter may help identify patients more likely to benefit from ICI therapy, while enabling closer monitoring of potential irAEs.