Background: Chronic inflammation mediated by poor genital hygiene is a well-recognized pathogenic trigger for penile squamous cell carcinoma (PSCC). The neutrophil-to-lymphocyte ratio (NLR) is a simple and reproducible factor reflecting the systemic inflammatory response and has been reported as an unfavorable indicator in PSCC. However, previous studies limited by small sample sizes, confounding prognostic features and without high-quality evidence to demonstrate the clinical significance of the NLR. Methods: A large cohort of 582 penile cancer patients who underwent radical inguinal lymphadenectomy with definitive pN stages were enrolled in this study. Univariate and multivariate Cox regression analyses were performed to investigate prognostic factors and inflammation-related markers in PSCC patients. More importantly, the propensity score matching (PSM) method was used to minimize the prognostic confounding clinicopathological features. Immunofluorescence was further used to investigate the correlation between tumor-infiltrating neutrophils, CD8⁺ T cells and the NLR. Results: According to the ROC curve, the optimal cutoff value for the NLR was 3.0, and 226 (38.8%) PSCC patients had a high NLR. Survival analyses indicated that advanced pT, pN, pathological grade, lymphovascular invasion, high NLR, C-reactive protein (≥ 2.2 mg/L) and serum amyloid A (≥ 11.3 mg/L) were associated with poor PFS and CSS. After PSM to eliminate interference from clinical factors, pN and the NLR were found to be independent prognostic indicators in PSCC patients (both p<0.001). Cox multivariate regression analysis revealed that the HR for PFS was 1.64 (1.15–2.34) in the high NLR group and 1.56 (1.04–2.34) in the high NLR group (p=0.006 and 0.030, respectively). PSCC patients with high NLRs experienced shorter PFS after receiving cisplatin-based chemotherapy (p=0.037) and PD-1 immunotherapy (p=0.020). In addition, we found that the infiltration of tumor-associated neutrophils (CD66⁺) and the CD8⁺ T-cell ratio were positively correlated with the NLR. The development and formation of neutrophil extracellular traps (NETs) might contribute to chemoresistance and tumor progression in high-NLR PSCC patients. Conclusions: In this study, we demonstrated that the NLR is an effective, simple and independent prognostic indicator for PSCC. The NLR holds promise as a powerful tool to guide decision-making in clinical practice.

PSM: propensity score matching; CSS: cancer specific survival; HR: hazard ratio; 95% Cl: 95% confidence interval; LVI: lymphovascular invasion; PNI: perineural invasion; NLR: neutrophil-lymphocyte ratio.