ABO Blood Groups and Risk of Cancer: a Systematic Review and Meta-analysis

Background: For decades, studies have been performed to evaluate the association between ABO bloodgroups and risk of cancer. However, whether ABO blood groups are associated with overall cancer risk remainsunclear. We therefore conducted a meta-analysis of observational studies to assess this association. Materialsand
Methods: A search of Pubmed, Embase, ScienceDirect, Wiley, and Web of Knowledge databases (to May2013) was supplemented by manual searches of bibliographies of key retrieved articles and relevant reviews.We included case-control studies and cohort studies with more than 100 cancer cases.
Results: The searchyielded 89 eligible studies that reported 100,554 cases at 30 cancer sites. For overall cancer risk, the pooled ORwas 1.12 (95%CI: 1.09-1.16) for A vs. non- A groups, and 0.84 (95%CI: 0.80-0.88) for O vs. non-O groups. Forindividual cancer sites, blood group A was found to confer increased risk of gastric cancer (OR=1.18; 95%CI:1.13-1.24), pancreatic cancer (OR=1.23; 95%CI: 1.15-1.32), breast cancer (OR=1.12; 95%CI: 1.01-1.24), ovariancancer (OR=1.16; 95%CI: 1.04-1.27), and nasopharyngeal cancer (OR=1.17; 95%CI: 1.00-1.33). Blood groupO was found to be linked to decreased risk of gastric cancer (OR=0.84; 95%CI: 0.80-0.88), pancreatic cancer(OR=0.75; 95%CI: 0.70-0.80), breast cancer (OR=0.90; 95%CI: 0.85-0.95), colorectal cancer (OR=0.89; 95%CI:0.81-0.96), ovarian cancer (OR=0.76; 95%CI: 0.53-1.00), esophagus cancer (OR=0.94; 95%CI: 0.89-1.00), andnasopharyngeal cancer (OR=0.81; 95%CI: 0.70-0.91).
Conclusions: Blood group A is associated with increasedrisk of cancer, and blood group O is associated with decreased risk of cancer.