A man's blood type can significantly influence prostate cancer relapse after successful surgery, study shows.
Men with group O blood are far less likely to suffer a recurrence of the disease following surgical intervention.
By contrast men with blood group A were shown by new research to be 35% more likely to fall victim to the disease again - even after surgery.
Prostate cancer is the most common form of cancer in European men and 40,000 cases are diagnosed in Britain annually.
Study author Dr Yoshio Ohno, of Tokyo Medical University, said: "This is the first time that anyone has shown that prostate cancer recurrence can vary with blood group.
"As yet, we don't know why the risks vary with blood group, but this work may guide us towards new avenues of molecular research on prostate cancer progression.
"Should we be counselling people with certain blood groups that they have a greater or lesser chance of recurrence, and should these risk factors be built into decisions on treatment?"
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The new research, presented at the European Association of Urology's (EAU) annual congress in Stockholm this week, tracked 555 patients with prostate cancer between 2004 and 2010.
An individual's blood group is determined by the presence of different antigens and antibodies. Antigens and antibodies serve as the blood's defences against foreign substances.
Group O blood is the most common in the UK with 44% of the population estimated to have the type. Roughly 42% of Britons have group A blood.
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Previously, different blood groups have been associated with different risk levels for developing certain cancers, such as gastric and pancreatic cancers.
EAU general secretary Professor Per-Anders Abrahamsson said: "This is an interesting first finding. There is great geographical variation in the incidence of prostate cancer, so there are obviously strong genetic factors at play.
"Blood groups have already been shown to be associated with prostate cancer incidence, now it looks like they might be associated with treatment outcomes as well."