Association Between Metabolic Score for Insulin Resistance and the Incidence of Gastric Cancer in South Korea: A Nationwide Retrospective Study

Background/Objectives: Insulin resistance (IR) is increasingly recognized as a factor associated with metabolic syndrome and various cancers. The metabolic score for insulin resistance (METS-IR) has emerged as a reliable surrogate marker for assessing IR. This study evaluated the association between the METS-IR and the gastric cancer (GC) incidence using data from a nationwide South Korean cohort. Methods: Data were obtained from the National Health Insurance Service (NHIS) cohort. A total of 318,336 participants aged ≥40 years who underwent a nationwide health screening between 2009 and 2010 were included and followed until GC diagnosis, death, or 31 December 2019. The METS-IR was calculated and categorized into quartiles. Hazard ratios (HRs) for GC incidence were estimated using Cox proportional hazards models. The analyses were adjusted for confounders, including age, sex, socioeconomic status, lifestyle factors, and comorbidities. Results: Participants in the highest METS-IR quartile (Q4) exhibited a significantly higher crude incidence of GC (2.26 per 1000 person-years) than those in the lowest quartile (Q1: 1.97 per 1000 person-years). Adjusted HRs showed a modest but statistically significant increase in GC risk in Q4 (HR: 1.10; 95% confidence interval: 1.02–1.19; p = 0.01) compared to Q1. Kaplan–Meier analysis revealed that participants with higher METS-IR levels had significantly shorter GC-free survival times than those in the lower quartiles. Restricted cubic spline analysis revealed a nonlinear relationship between the METS-IR and GC risk, with higher METS-IR levels associated with an increased risk. Conclusions: An elevated METS-IR was associated with an increased GC risk, suggesting its potential utility in stratifying GC risk. The METS-IR may help identify high-risk individuals and support GC prevention.