Perspectives: Neutrophil-to-lymphocyte Ratio as a Potential Biomarker in Immune Checkpoint Inhibitor for Non-Small-Cell Lung Cancer.

There is a rising need for optimal biomarkers to better tailor treatments for patients with cancer in the era of immunotherapy. In addition to programmed death-ligand 1 (PD-L1) and tumor mutation burden (TMB), neutrophil-to-lymphocyte (NLR) is regaining interest as a biomarker in immunotherapy for its availability, accessibility, and reproducibility. High NLR, according to different thresholds, is consistently reported to correlate with poor prognosis in different treatments in several cancers. Yet, most data come from retrospective analysis, and proof of mechanism and principle evaluations are limited. Prospective studies or adequately sized retrospective analyses of prospectively collected data are required to best assess its role in clinical practice. Moreover, effective myeloid or neutrophil modulators in tumor microenvironment can potentially contribute as a new therapeutic strategy. This perspective will summarize our current knowledge and will discuss where we stand now and propose future directions.