Background: Colon cancer is a leading cause of cancer-related mortality worldwide. Despite advances in multimodal therapies, recurrence remains a significant challenge, and patient outcomes vary widely. While traditional TNM staging and molecular markers (e.g., MSI, RAS/BRAF) are established prognosticators, extensive research has been conducted on systemic inflammatory markers due to their clinical relevance. The Neutrophil-to-Lymphocyte Ratio (NLR), easily accessible via routine blood tests, is a practical tool for evaluating the impact of systemic inflammation on clinical outcomes.
Objectives: This study aims to evaluate the prognostic impact of the preoperative NLR on overall survival (OS) in Korean patients with colon cancer.
 
Methods: A total of 5,265 patients who underwent surgical resection for colon cancer at Seoul National University Hospital between January 2002 and December 2015 were included in the analysis. Preoperative blood samples were collected from all patients to determine baseline NLR levels. The NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. NLR levels were then categorized into tertiles based on the distribution of the study population. Overall survival (OS) was defined as the period from the date of surgery to the date of death or the last follow-up. Hazard ratios (HRs) and 95% confidence intervals (CIs) for survival outcomes were estimated using Cox proportional hazards regression models, adjusting for potential confounding factors, including age, sex, BMI, American Society of Anesthesiologists (ASA) physical status classification system, and pathologic T stage and N stage.
 
Results: A total of 1,908 deaths were recorded among the 5,265 patients during the follow- up period. In the fully adjusted model, the highest NLR tertile (T3) was significantly associated with an increased risk of mortality (aHR = 1.61; 95% CI, 1.43–1.81) compared with the lowest tertile (T1). In sex-stratified analyses, these associations remained significant in both sexes (men: aHR= 1.68; 95% CI, 1.46–1.95, women: a HR= 1.45; 95% CI, 1.19–1.77)
 
Conclusion: This study demonstrates that a high preoperative NLR is an independent and significant predictor of for OS in Korean patients with colon cancer. While the association was observed in both sexes, the impact of systemic inflammation on survival outcomes was particularly pronounced in men. Given that NLR is derived from a routine, inexpensive, and minimally invasive blood test, it may serve as s a practical clinical biomarker for risk stratification.