ABO blood group and cancer

Background: ABO blood type has been associated with various malignancies, including pancreatic cancer. Our aim was to study this association using data from a hospital-based tumour registry. Methods: From the tumour registry, we retrieved data from 15,359 cancer patients treated during 2000-2003 at the European Institute of Oncology (Milan, Italy), with defined ABO blood type. We performed a case-control analysis, comparing the distribution of ABO blood types of patients with each specific form of cancer against that of patients with other forms of cancer. We also reviewed the literature and performed a meta-analysis on the association between ABO blood group and pancreatic cancer. Results: We observed a significantly lower frequency of blood type O in patients with exocrine pancreatic cancer compared to patients with other forms of cancer (29% versus 44%; P <0.001; odds ratio (OR), 0.53; 95% confidence intervals (CI), 0.33-0.83). This association was confirmed by the meta-analysis of seven prior studies (summary relative risk, 0.79; 95% CI, 0.70-0.90). No association was found for endocrine pancreatic cancer or for cancer originating in other organs. Conclusions: Our data suggest that the association between ABO blood group and cancer is limited to exocrine pancreas malignancy.