Peripheral blood eosinophilia may be a prognostic biomarker in non-small cell lung cancer patients treated with immunotherapy

Background Eosinophils have been traditionally associated with the initiation and propagation of inflammatory responses, particularly in allergic diseases and helminth infections. More recently, an association between eosinophils and cancer has been the focus of several studies, but controversial results have emerged. This study aims to evaluate the prognostic role of peripheral blood eosinophilia in non-small cell lung cancer (NSCLC) patients receiving immunotherapy (IO). We also evaluated the impact of peripheral eosinophilia on the occurrence of immune-related adverse effects (irAEs). Methods Advanced NSCLC patients under IO were included in a retrospective single-center study. Peripheral blood eosinophilia was defined by a count greater than 500/µL. Patients were analyzed for eosinophil counts, overall survival (OS), progression-free survival (PFS), overall response rate (ORR) and disease control rate (DCR). Results A total of 121 NSCLC patients receiving IO were included. Thirty-three (27.3%) patients presented peripheral blood eosinophilia during treatment. Patients with peripheral eosinophilia presented more frequently non-progression as best overall response to IO (83.3% vs. 58.1%, P=0.014), higher median OS (26.6 vs. 9.5 months, P=0.022) and higher median PFS (13.8 vs. 4.6 months, P=0.013). IrAEs were more common in patients with peripheral eosinophilia (66.7% vs. 36.4%, P=0.003). Conclusions This study suggests that peripheral blood eosinophilia may predict better outcomes in NSCLC patients receiving IO, despite being associated with an increased risk of irAEs. According to our findings eosinophils may be involved in immune response against tumor. Routine eosinophils count assessment may be an additional prognostic tool in NSCLC patients receiving IO.