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.

In some populations, other findings vary. For instance, a study of Chinese men found that blood group B had a lower risk of gastrointestinal cancers than group A, highlighting how results can differ by region and genetics.

Overall, blood group O appears to offer the lowest relative cancer risk across many cancer types, although the differences are modest. One analysis estimated that people with blood group A had about a 19 percent higher risk of stomach cancer compared to group O.

Importantly, these are associations, not proof of causation. Factors such as diet, smoking, infections like H. pylori, and environment strongly influence cancer development and may explain much of the variation.

The link also depends on cancer type: for some, like breast cancer, large studies have found no meaningful relationship with ABO blood group.

Having blood group O does not guarantee protection — it only suggests a slightly lower statistical risk in some studies. Lifestyle choices, screenings, and family genetics remain far more powerful predictors of cancer.

In short: current evidence points to blood group O as having the lowest average cancer risk, but maintaining healthy habits and regular medical checkups matter far more for prevention.