Prognosticating role of serum eosinophils on immunotherapy efficacy in patients with advanced melanoma

Aim: To evaluate serum eosinophilia (≥500 peripheral eosinophil counts/microliter) in prognosticating immunotherapy (IO) efficacy. Methodology: A retrospective study of 86 patients with advanced melanoma on PD-1 inhibitors. Results: Eosinophilia-on-IO was an independent prognosticating factor for median OS (HR :0.223; 95% CI: 0.088-0.567; p = 0.002). 'Late eosinophilia' (≥1 year from IO start date) group had better median OS (31.9 vs 24.1 vs 13.0 months; p = 0.002) when compared with 'early eosinophilia' (<1 year from IO start date) and 'no eosinophilia' groups, respectively. Conclusion: Eosinophilia-on-IO and its timing were associated with better IO efficacy in patients with advanced melanoma. Our findings provided insights on potential therapeutic benefit of inducing eosinophilia at certain interval time to obtain a longer durable immunotherapy response.