The surprising finding worried doctors, who say women will now have to talk seriously with their physicians about the risk of taking a daily aspirin.
Pancreatic cancer affects only 31,000 Americans a year, but it kills virtually all its victims within three years.
The study of 88,000 nurses found that those who took two or more aspirins a week for 20 years or more had a 58 percent higher risk of pancreatic cancer.
Researchers expected that aspirin would protect against pancreatic cancer, especially since its preventive role in colorectal cancer has been well documented. However, now it appears that the need to examine the relationship more thoroughly is required.
This finding does not mean that women should no longer use aspirin. There are still important benefits to the drug; we also need other large cohort studies to confirm our finding before we can draw any conclusions say researchers.
They studied 88,378 women taking part in a large and wide-ranging study of nurses and their health.
Over 18 years, 161 of the nurses developed pancreatic cancer.
Those who took 14 tablets or more per week had an 86 percent greater risk of pancreatic cancer than non-users. The nurses who took between six and 13 tablets had a 41 percent higher risk, while those who only took one to three aspirins a week had an 11 percent greater risk.
The women who took the most aspirin said they were taking it not to protect against heart disease, but because of headaches or other aches and pains.
Even with the increased risk, heart disease is a much greater threat to a woman's, or a man's, health. It is by far the biggest killer in the United States and other developed nations. The American Heart Association says cardiovascular disease killed more than 945,000 Americans in 2000.
Doctors do not clearly understand what causes pancreatic cancer, or what makes it so deadly. Obesity is another risk factor, but researchers findings were held regardless of a woman's weight, whether she smoked and whether she had diabetes.
According to research one study showed that regular aspirin use may cause pancreatitis -- an inflammation of the pancreas that can sometimes lead to pancreatic cancer.
Thus researchers conclude that there is urgent need to settle the biologic reasons for pancreatic cancer.