Absolute Increase in the Number and Proportion of Peripheral Eosinophils Associated With Immune Checkpoint Inhibitor Treatment in Non-small Cell Lung Cancer Patients

Background/Aim: To clarify the clinical significance of the absolute increase in the number and proportion of peripheral eosinophils associated with immune checkpoint inhibitor (ICPI) treatment in non-small cell lung cancer (NSCLC) patients. Patients and Methods: We performed a retrospective study, by reviewing the medical charts of 191 patients who were treated with ICPI monotherapy and 80 patients treated with the combination of ICPI and chemotherapy during the period from February 2016 and April 2021. Results: In patients treated with ICPI monotherapy, there was a significant difference in time to treatment failure (TTF) between the two groups divided by eosinophils ≥ or <10%. Similarly, a significant difference was found in TTF between the two groups divided by eosinophils ≥ or <1,500/μl. Factors related to both an increase in the number and percentage of peripheral eosinophils were “immune-related adverse effects (irAE) that did not lead to discontinuation of administration". Conclusion: Some patients with irAE might have a 'favorable' absolute increase in peripheral eosinophils.