Role of eosinophilia in patients with recurrent/metastatic head and neck squamous cell carcinoma treated with nivolumab: Prediction of immune-related adverse events and favorable outcome

Introduction Immune-related adverse events (irAEs) are prognostic factors for patients on nivolumab. However, predictors of irAEs have not yet been identified. We aimed to investigate the predictors of irAEs occurrence and nivolumab discontinuation due to irAEs.Methods Sixty-two patients with recurrent/metastatic head and neck squamous cell carcinoma received nivolumab therapy between June 2017 and December 2020. Treatment outcome was compared between the groups with or without irAEs. The irAE (+) group was further divided by nivolumab discontinuation. Progression-free survival (PFS) and overall survival (OS) were compared between the groups. Predictors of irAE occurrence were analyzed.Results Twenty-one patients (33.9%) developed irAEs, and six (28.6%) discontinued nivolumab due to severe irAEs. The irAE (+) group had significantly longer PFS and OS than the irAE (-) group (median PFS, 12.7 vs. 1.9 months; median OS, 33.1 vs. 12.8 months). The treatment outcomes in the discontinuation group were comparable to those in the non-discontinuation group. The maximum absolute eosinophil count (AEC) during nivolumab therapy was significantly higher in the irAE (+) group than in the irAE (-) group (548.8 vs. 182) and higher in the discontinuation group than in the non-discontinuation group (729.3 vs. 368.6). The receiver operating characteristic curve showed that the maximum AEC had a moderate-to-high accuracy for predicting irAE occurrence (area under the curve [AUC], 0.757) and nivolumab discontinuation (AUC, 0.893).Discussion Monitoring AEC during nivolumab therapy may be useful in predicting irAE occurrence, nivolumab discontinuation, and disease prognosis.