Association between ABO blood group and survival in patients with esophageal, gastric, and colorectal cancer: a systematic review and meta-analysis

: The ABO blood group, has been investigated as a prognostic factor in esophageal, gastric and colorectal cancer, with conflicting results. We conducted a systematic review and meta-analysis to assess the effect of ABO blood type on overall survival (OS). We searched PubMed and Embase from inception to February 2026 following Preferred Reporting Items for Systematic reviews and Meta-Analysis guidelines. Two reviewers independently screened studies reporting hazard ratios for OS across ABO blood group pairwise comparisons. Summary hazard ratios (SHRs) were estimated using random-effects models. Heterogeneity was assessed via the I2 index. Study quality and publication bias were evaluated. Twenty-three studies were included, covering over 24 000 patients. For esophageal cancer, blood group A was associated with significantly lower mortality compared with group O [SHR: 0.89, 95% confidence interval (CI): 0.83-0.95]. Group AB was associated with increased mortality compared with group A (SHR: 1.36, 95% CI: 1.09-1.70) and group B (SHR: 1.26, 95% CI: 1.00-1.59). Subgroup analyses revealed that blood group AB was associated with lower mortality in high-quality gastric cancer studies, and that blood group B was associated with significantly lower mortality compared with group A in colorectal cancer when excluding the single low-quality study (SHR: 0.70, 95% CI: 0.59-0.84), consistent with the subgroup analysis restricted to Asian studies (SHR: 0.64, 95% CI: 0.51-0.81). Our findings suggest that blood group A vs. O is associated with lower mortality in esophageal cancer and that blood group AB is associated with lower mortality in gastric cancer among high-quality studies. However, future studies are needed to confirm these findings.