9551 Background: Despite the implementation of immune checkpoint inhibition (ICI) for patients with metastatic melanoma, there remains an unmet clinical need for predictive/prognostic biomarkers to determine, from outset, which patients will derive benefit. Recent literature has suggested a significant role for granulocyte subsets in the development of resistance to systemic therapies, with an associated role in adaptive immunity. Methods: We sought to establish a novel immunological scoring system to use as a predictive/prognostic biomarker in patients with advanced melanoma being treated with ICI. In this retrospective, single centre study evaluating patients with advanced melanoma treated with combination ipilimumab and nivolumab, progression free survival (PFS) and overall survival (OS) were compared between groups defined by neutrophil, lymphocyte, eosinophil, monocyte and basophil counts. Data from 226 patients was collected at baseline, week 3, week 6, first response scan and at progression. Baseline and week 3 data was the focus of this primary analysis. Kaplan-Meier estimation and Cox regression analysis were performed. Results: Univariate analysis demonstrated that absolute neutrophil, eosinophil and basophil count strongly associates with PFS and OS outcomes at week 3. Combination of these counts into a novel neutrophil to eosinophil + basophil ratio (NEBR, (N/(E+B)) was assessed as a scoring system. High NEBR was associated with poorer PFS and OS at baseline and week 3 with consistently superior predictive/prognostic value than the well-established neutrophil to lymphocyte ratio (NLR). After accounting for covariates including concurrent steroids, infection and LDH, high NEBR remained significantly associated with worse PFS at baseline and poorer PFS and OS at week 3. Conclusions: Our findings highlight NEBR as a novel immunotherapeutic predictive/prognostic biomarker with potential clinical utility that warrants further investigation in patients with advanced melanoma and across other tumour groups. Further validation will be required through independent external datasets. [Table: see text]
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