Pre-Treatment Neutrophil-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Ratio as Prognostic Biomarkers for Sentinel Lymph Node Positivity and Recurrence-Free Survival in Primary Cutaneous Melanoma: An Exploratory Single-Centre Retrospective Cohort Study

Background and Objectives: Systemic inflammation contributes to melanoma progression, yet the prognostic value of routinely available inflammatory ratios remains insufficiently characterized in real-world cohorts. We evaluated whether pre-treatment neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are independently associated with sentinel lymph node (SLN) positivity, histopathologic aggressiveness, and recurrence-free survival (RFS) in primary cutaneous melanoma. Methods: In this single-center, retrospective, exploratory, observational cohort, 87 adults with histologically confirmed primary cutaneous melanoma were stratified by pre-treatment NLR using a cut-off of 3.0 into low-NLR (n = 47) and high-NLR (n = 40) groups. Outcomes included Breslow thickness, ulceration, mitotic rate, AJCC stage, SLN status, and RFS over a median follow-up of 38.4 months. Discrimination was assessed by receiver operating characteristic (ROC) analysis, time-to-event endpoints by Kaplan–Meier and Cox proportional-hazards modelling, and SLN positivity by multivariable logistic regression. Results: High-NLR patients had thicker (median 2.1 vs. 0.8 mm, p < 0.001), more frequently ulcerated (42.5% vs. 12.8%, p = 0.003), and more advanced melanomas (early stage 27.5% vs. 68.1%, p < 0.001). SLN positivity among biopsied patients was 35.5% vs. 8.7% (p = 0.027). For RFS, NLR ≥ 3.0 carried a univariable hazard ratio (HR) of 4.32 (95% CI 1.60–11.67) and remained independently prognostic after multivariable adjustment (adjusted HR 2.87, 95% CI 1.04–7.92, p = 0.042). An NLR + PLR composite outperformed Breslow thickness for predicting SLN positivity (AUC 0.829 vs. 0.702, DeLong p = 0.041). Conclusions: In this exploratory, single-center retrospective cohort, pre-treatment NLR and PLR were inexpensive, widely available biomarkers that were associated with prognostically relevant melanoma features and outcomes. These hypothesis-generating findings suggest that inflammatory ratios could complement conventional histopathologic predictors, but they were derived and tested within a single small cohort without independent validation and require confirmation in larger, prospective, multi-center studies before any clinical application.