Eosinophil may be a predictor of immune‐related adverse events induced by different immune checkpoint inhibitor types: A retrospective multidisciplinary study

Abstract Background Immune checkpoint inhibitors (ICIs) can cause severe immune‐related adverse events (irAEs). However, biomarkers for irAEs common to different types of ICIs and cancers have not been reported. This study examined whether eosinophils can be used as a predictor of irAEs. Methods Six hundred fourteen patients with cancer (esophageal, gastric, head and neck, lung, melanoma, renal cell, urothelial, and other cancer) received anti‐PD‐1, anti‐PD‐L1, or anti‐CTLA‐4 plus anti‐PD‐1 therapy. The patients were divided into two groups depending on whether they experienced irAEs (irAE group) or not (non‐irAE group). Eosinophils were examined before the two‐course treatment. Results Patients in the irAE group who received anti‐PD‐1 or anti‐CTLA‐4 plus anti‐PD‐1 therapy had higher eosinophils before the two‐course treatment than those in the non‐irAE group (p < 0.05). The eosinophils in the anti‐PD‐L1 therapy group tended to increase in the irAE group. Furthermore, eosinophils in gastric, head and neck, lung, melanoma, renal, and urothelial cancers were significantly higher in the irAE group than in the non‐irAE group (p < 0.05). The optimal cutoff value for eosinophils against irAEs was 3.0% (area under the curve = 0.668). In multivariate analyses, eosinophils of ≥3.0% were an independent factor for irAEs (odds ratio: 2.57, 95% CI: 1.79–3.67). Conclusion An increased eosinophil before the two‐course treatment may be a predictor of irAEs in various cancers treated with different ICIs