INTRODUCTION: The associations between ABO blood group and cancer risk have been studied repeatedly, but results have been variable. Consistent associations have only been reported for pancreatic and gastric cancers.

MATERIALS AND METHODS: We estimated associations between different ABO blood groups and site-specific cancer risk in a large cohort of healthy blood donors from Sweden and Denmark.

RESULTS: A total of 1.6 million donors were followed over 27 million person-years (20 million in Sweden and 7 million in Denmark). We observed 119,584 cancer cases. Blood groups A, AB and B were associated either with increased or decreased risk of cancer at 13 anatomical sites (p≤0.05), compared to blood group O. Consistent with assessment using a false discovery rate approach, significant associations with ABO blood group were observed for cancer of the pancreas, breast, and upper gastrointestinal tract (mouth, salivary glands, pharynx, esophageal adenocarcinoma and stomach).

DISCUSSION: Our study reconfirms the association between ABO blood group and cancer risk and exact underlying mechanisms involved needs further research.