Pretreatment eosinophil counts as a predictive biomarker in non-small cell lung cancer patients treated with immune checkpoint inhibitors

Background: The peripheral blood eosinophil count prior to treatment has potential as a predictive biomarker for a beneficial clinical response to cancer immunotherapies. Therefore, the present study investigated the impact of the eosinophil count on overall survival (OS) in non-small cell lung cancer (NSCLC) patients treated with immune checkpoint inhibitors (ICI). Methods: We retrospectively reviewed all patients diagnosed with NSCLC and treated with ICI monotherapy between March 2016 and August 2021 at National Hospital Organization Kochi Hospital and Tokushima University. Results: A total of 166 patients were included. Fifty-five patients had an eosinophil count of less than 100 cells/mu L (Eo < 100). Nighty-eight patients had an eosinophil count of 100 cells/mu L or more, but less than 500 cells/mu L (100 <= Eo < 500). Thirteen patients had an eosinophil count of 500 cells/mu L or more (Eo >= 500). The median OS of all lung cancer patients was 476 days. The median OS of lung cancer patients with Eo <100, 100 <= Eo <500, and Eo >= 500 was 339, 667, and 143 days, respectively. A Kaplan-Meier univariate analysis showed a significant difference in OS between these three groups (p < 0.001). A Cox proportional regression analysis identified 100 <= Eo <500 (p = 0.04), ECOG PS score >= 2 (p = 0.02), tumor size >= 5 cm (p = 0.02), and PD-L1 = 1% (p = 0.01) as independent predictors of OS. Conclusion: OS was significantly longer in ICI-treated NSCLC patients with a pretreatment eosinophil count of 100 <= Eo <500 than in the other patients and, thus, has potential as a new predictive biomarker.