BOSTON — A study raises the possibility that frequent use of Aspirin, long thought to prevent some kinds of cancer, may actually increase the likelihood of pancreatic tumours, although researchers caution that more study is needed to be sure.

The research, part of the highly regarded Nurses Health Study at Boston's Brigham and Women's Hospital, came to the unexpected conclusion that women who take Aspirin twice daily may have nearly double the risk of this rare form of cancer.

Evidence is building that regular Aspirin use can reduce the risk of colon cancer, which is three times more common than pancreatic cancer. Aspirin is also routinely recommended to prevent heart attacks. The new results also contradict another large study of Aspirin and pancreatic cancer that was reported last year.

"This finding does not mean that women should no longer use Aspirin," said Dr. Eva Schernhammer, one of the researchers. "There are still important benefits to the drug."

She said other large studies are needed before experts can draw any conclusions about this potential hazard.

The study, based on a long-running followup of more than 88,000 female nurses, was presented Monday in Phoenix at a meeting of the American Association for Cancer Research.

The study found that women who reported 20 or more years of regular Aspirin use, with an average intake of at least 14 tablets tablets a week, had an 86 per cent increased risk of pancreatic cancer, compared to those who did not take Aspirin.

Last year, researchers from the University of Minnesota reported a similar followup of more than 28,000 women in the Iowa Women's Health Study. Contrary to the Boston researchers, they found a 43 per cent lower rate of pancreatic cancer among Aspirin users.