Blood type could matter in pancreatic cancer

People with type O blood are less likely to develop cancer of the pancreas than are people with type B blood, a study finds. People with type A or AB blood face a risk that falls somewhere in between, researchers report in the March 18 Journal of the National Cancer Institute.

Research suggesting that blood type might influence cancer risk first emerged in the 1950s, and the idea has puzzled scientists ever since.

Because testing blood type was relatively easy to do even then, scientists did it, says study coauthor Brian Wolpin, an oncologist and epidemiologist at the Dana-Farber Cancer Institute and Harvard Medical School in Boston. But reports over the past half-century have offered a mixed bag — some suggest blood type matters in cancer and others indicate it doesn’t.

In the new study, Wolpin and his colleagues tapped into a database of medical information about more than 100,000 nurses and other health professionals. The data revealed each participant’s blood type, any diagnosed diseases and a host of other health and lifestyle factors. The researchers found that 316 participants developed pancreatic cancers between 1996 and 2005.

Compared with the percentage of participants with type O blood who developed the cancer, people with type A were 32 percent more likely, those with type AB were 51 percent more likely and those with type B faced a 72 percent greater risk. The researchers accounted for age, gender, physical activity, weight and smoking status, factors that might bias the data.

It remains unclear why blood type might be associated with pancreatic cancer risk, but the answer could lie with the gene that orchestrates blood type or with neighboring genes, Wolpin says.

Four blood types exist because people have one of four arrays of glycoproteins on red blood cells. Type O people actually lack these compounds, whereas people with another blood type have that type’s distinct combination.

Wolpin says the findings seem to suggest that these glycoproteins on the surface of cells might affect cancer risk. Thus, the ABO gene, which encodes the glycoproteins, would modulate the risk.

Or perhaps not. The variant forms of ABO that give rise to the four blood types might instead result from variants in other genes that are near ABO on chromosome 9, he says. The still-unidentified proteins encoded by those genes “might be the true effecter molecules,” Wolpin speculates. “Blood type might be a marker and not causal.”

Pathologist Visalam Chandrasekaran of the New York Blood Center believes this study shows only a modest association between blood type and pancreatic cancer risk, and therefore doesn’t establish that people with type O blood are at any less real risk of pancreatic cancer than someone with type B blood. “But this is an observation that I will keep in the back of my mind,” she says. If further evidence arises that ties into this finding, “I’ll see if the two go together.”