Large scientific reviews and cohort studies suggest that people with blood group O generally have a lower risk of developing certain cancers compared with non-O groups (A, B, AB). One meta-analysis summarized it clearly: “Blood group A is associated with increased risk of cancer, and blood group O is associated with decreased risk.”
For specific cancers, the pattern appears most consistent with stomach and pancreatic cancers. Studies show that people with blood group A or AB face a higher risk of gastric cancer than those with blood group O. Similarly, pancreatic cancer risk tends to be greater among non-O blood types.