Association between ABO blood groups and gastric cancer outcomes: a Kaplan-Meier-derived patient data meta-analysis

Background Gastric cancer (GC) remains the fifth most common and lethal cancer worldwide, often diagnosed at advanced stages, with limited treatment options and poor survival. Beyond established risk factors, the ABO blood group system has been suggested as a potential prognostic factor, but evidence remains inconclusive.Methods Medline, Scopus, and Web of Science were searched to 27 July 2025, for studies including GC patients with reported overall survival (OS) stratified by blood types O, A, B, and AB. Kaplan–Meier curves from eligible studies were digitized to reconstruct individual patient data, which were pooled to estimate median OS and hazard ratios (HR) using Cox regression.Results Seven studies comprising 8,726 GC patients were included (O: 3,693; A: 946; B: 605; AB: 315). Median OS was highest for type O (85.1 months, 95% CI 77.5–86.4) and AB (78.2 months, 95% CI 73.9–NA), and lowest for type A (20.0 months, 95% CI 17.9–21.9) and B (35.5 months, 95% CI 27.9–78.5). Compared with non-O, type O had a significantly better prognosis (HR 0.63; p < 0.0001). Type A (HR 1.85; p < 0.0001) and type B (HR 1.20; p = 0.0018) were associated with worse survival, while type AB showed a favorable prognosis compared to non-AB (HR 0.83; p = 0.039).Conclusion ABO blood group is a significant prognostic factor in GC, with types A and B linked to poorer survival.