Compared with the general population, individuals with gastric cancer (GC) experience higher rates of atrial fibrillation (AF) and cardiovascular death. Yet, the influence of cancer stage on AF development has not been well defined. This research assessed how GC stage, classified by the Surveillance, Epidemiology, and End Results (SEER) system, relates to AF risk. A retrospective cohort analysis was conducted using anonymized data from South Korea’s Cancer Public Library Database, including patients diagnosed with GC between 2012 and 2019 and followed until 2020. The likelihood of AF occurrence was analyzed across SEER categories (localized, regional, distant) by estimating adjusted hazard ratios (aHRs) with 95% confidence intervals (CIs). Stratified analyses were performed according to age, gender, diagnosis year, and comorbid diseases. Among 211, 500 eligible participants, 7266 developed AF during follow-up. A stage-dependent trend was observed, where AF risk rose with disease progression: aHR 2.00 (95% CI 1.81-2.22) in distant-stage and 1.32 (95% CI 1.25-1.41) in regional-stage GC, compared with localized cancer. These trends were consistent across all subgroups and particularly marked among younger patients, females, and those without hypertension. AF incidence in GC patients correlates with the initial cancer stage. Intensive AF screening and preventive management may be beneficial for individuals with advanced-stage GC to improve long-term outcomes.
