Some studies have suggested a weak association between
certain blood types (specifically blood type A) and an increased risk of
pancreatic cancer, but this link is still being investigated.
There are many blood groups i.e., types of blood. However,
the four main blood types include A, B, AB and O. Your blood group is
determined by the genes you inherit from your parents. Each group can be either
RhD positive or RhD negative, which means in total there are 8 blood groups.
Dana-Farber Cancer Institute Research, 2009
Offering a novel clue about the basic biology of pancreatic
cancer, researchers at Dana-Farber Cancer Institute have confirmed a
decades-old discovery of a link between blood type and the risk of developing
the disease.
The finding, published online by the Journal of the National
Cancer Institute, is based on an analysis of blood type and pancreatic cancer
occurrence in participants of two large health-tracking studies, the Nurses’
Health Study and the Health Professionals Follow-Up Study.
The new study demonstrates that while people’s overall risk
of pancreatic cancer is relatively low — with nearly 40,000 new cases diagnosed
annually in the United States, compared with nearly 150,000 new cases of
colorectal cancer — people with blood types A, B, or AB were more likely to
develop the disease than those with type O.
“Except for several rare familial syndromes, the genetic
factors that raise or lower an individual’s risk for pancreatic cancer are
largely unknown,” said the study’s lead author, Brian Wolpin, an instructor in
medicine at Harvard Medical School. “Studies done several decades ago suggested
a link between blood type and the risk of various malignancies, including
pancreatic cancer, but they were limited by the fact that they ‘looked back’ at
cancers that had already occurred and involved relatively few cases. We wanted
to see if the association held up using modern patient cohorts and research
techniques.”
They found that, compared to participants with type O blood,
those with type A had a 32 percent higher chance of incurring pancreatic
cancer, those with type AB had a 51 percent higher chance, and those with type
B had a 72 percent higher chance.
Within the entire group, 17 percent of pancreatic cancers
were attributable to inheriting a non-O blood group. But because the lifetime
risk of developing the disease is relatively low (estimated at 1.3 percent) and
the increased risk associated with blood type relatively modest, screening
tests for pancreatic cancer risk are unlikely to be based on blood type alone.
The real value of the findings is what they suggest about the inner workings of
the disease, the authors say.
The four human blood groups are defined by the type of
glycoproteins — confections of sugar and protein — found on the surface of red
blood cells and other cells, including those in the pancreas. A gene known as
ABO helps construct these glycoproteins by ordering the placement of sugar
molecules on a protein “backbone” called the H antigen. The pattern formed by
these sugars determines whether an individual’s blood type is A, B, AB, or O.
(In the O type, no sugars are attached to the antigen.)
Experiments by other investigators have shown that normal
pancreas cells carry a different pattern of these blood-type antigens than
pancreatic tumor cells do, suggesting that changes in the ABO gene’s activity
may occur as the cells become cancerous. Researchers speculate that alterations
in the antigens may interfere with the cells’ ability to signal and adhere to
one another, and with the immune system’s ability to detect abnormal cells —
potentially setting the stage for cancer.
Blood-type antigens may also affect the level of
inflammatory proteins in a person’s blood. Chronic inflammation has been linked
to pancreatic cancer risk.
Intriguing as these findings are, they don’t necessarily
prove a direct link between blood-type antigens and pancreatic cancer
development, the authors assert. It is also possible that the ABO gene is
merely a marker for other, nearby genes that are more directly involved in
cancer development.
“The association between blood type and pancreatic cancer
risk provides a new avenue for getting at the biological mechanisms that
underlie the disease,” Wolpin says. “Understanding the biology will put us in a
better position to intervene so the cancer doesn’t develop or progress.”
The study’s senior author is Charles Fuchs of Dana-Farber
and Brigham and Women’s Hospital (BWH). Co-authors include David Hunter and
Edward Giovannucci of BWH and the Harvard School of Public Health (HSPH);
Andrew Chan of BWH and Massachusetts General Hospital; Patricia Hartge and
Stephen Chanock of the National Cancer Institute; and Peter Kraft of the HSPH.
PLOS One Study, 2017
Other studies, carried out using a similar methodology,
however, have come to different findings concerning blood type B and the risk
of different cancers.
In 2017, research published in the journal PLOS One
assessed the risk of different blood types in relation to colorectal cancer -
the fourth most common cancer in the UK.
There are over 41,000 new cases of the disease diagnosed
each year, according to Cancer Research UK’s bowel cancer statistics.
The researchers wrote that “compared with blood type A,
blood type B was associated with statistically significant reduced risk of all
cancers.
“Both blood types B and AB were associated with
significantly lower risk of gastrointestinal cancer and colorectal cancer
respectively".
According to the results, type B blood was also
associated with a significantly lower risk of stomach and bladder cancer too.
Blood type AB, however, was associated with a
significantly increased risk of liver cancer.
Haukeland University Hospital, 2018
PhD candidate Khadija El Jellas and his colleagues at
Haukeland University Hospital compared blood types in people from western
Norway who had pancreatic cancer with two different groups of people from the
same region.
The results showed that there appears to be a correlation
between a person’s blood type and the risk of the disease.
“We found that people who have blood type A have a
slightly increased risk, while those with blood type 0 are slightly more
protected than the average,” says Anders Molven, a professor at the University
of Bergen who is head of the research group at Haukeland.
Molven emphasizes, however, that these differences in
risk are quite small. People with blood type O can still get pancreatic cancer,
and the risk of getting this type of cancer is still small for people with
blood type A.
Nevertheless, this connection may open the door on what
lies behind this frightening disease.
Models Assessment
Intestinal flora
It seems reasonable that your blood type might affect
your risk of blood cancer, but links between blood type and pancreatic cancer
could seem a little more farfetched.
But the researchers think one explanation may be related
to a person’s intestinal bacteria.
Different blood types mean that one person’s blood cells
are not exactly the same as another person’s. In addition to having differences
in the proteins in the blood cells, different blood types have different sugar
molecules in the blood.
People with blood types A and B have an extra sugar
molecule in their blood compared to people with blood type O. This is why
doctors match blood types when they do blood transfusions.
If a person with type O blood receives type A blood, their
immune system perceives the sugar molecules as foreign and mounts a strong
immune response.
However, subsequent research has shown that these
particular sugar molecules are also found on certain cells in the intestine. As
a result, different kinds of intestinal bacteria attach to different degrees on
intestinal cells containing A, B or O molecules.
“There is pretty good evidence that different blood types
can cause differences in a person’s intestinal flora. It is also known that the
intestinal flora can affect some types of cancer. It’s possible to imagine that
a blood type changes the intestinal flora, which in turn affects the risk of
pancreatic cancer,” Molven says.
Immune system
Another hypothesis concerns the immune system itself.
Our immune systems are important in the body's ability to
fight cancer.
Molven says that cancer cells often change molecules that
are found on the surface of the cell. And sometimes they may be changed to
resemble the sugar molecules found on blood cells, for example A.
In that case, the immune system of a human with blood
type A will not perceive the cancer cell as foreign. On the other hand, the
immune system of someone with type O blood would recognize the cancer cells as
foreign and would fight them.
Digestive enzymes
“We have also studied one of the digestive enzymes that
are produced and excreted in the pancreas,” Molven explains.
It turned out that this enzyme also had sugar molecules
on its surface that were associated with blood type.
“There is thus a common pancreatic enzyme that is
modified according to the blood type. Now we wonder if this has anything to do
with the risk of cancer,” he said.
Perhaps this enzyme affects cancer risk by influencing
intestinal flora? Molven believes the findings regarding the enzyme may be
compatible with the hypothesis related to the intestinal flora and the immune
system. Perhaps even both at the same time.
Even though these hypotheses are unproven, Professor
Caroline Verbeke at the University of Oslo is optimistic. She is head of
Pancreatic Cancer Network Norway, which works for better treatment of
pancreatic cancer.
“These results are interesting because they link things
that we haven’t seen in this context before,” she said. “First and foremost, it
is important to know more about the risk factors for pancreatic cancer. Most
people can't do anything about their risk, like genes. But if your risk is also
affected by microorganisms in the digestive system, it may be possible to
influence them.”
Sources and Additional Information:
https://news.harvard.edu/gazette/story/2009/03/blood-types-indicate-greater-risk-for-cancer/
https://www.express.co.uk/life-style/health/1629706/cancer-warning-blood-type-increases-risk
