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BMJ. 2007 April 21; 334(7598): 816.
PMCID: PMC1853190

Aspirin reduced risk of cancer in large US study

A new prospective cohort study adds to the evidence that regularly taking aspirin reduces the incidence of cancers and cancer mortality. But the study, in postmenopausal women in the US Midwest, found that use of non-steroidal anti-inflammatory drugs did not protect against cancer.

Researchers from the Mayo Clinic College of Medicine in Rochester, Minnesota, and the University of Minnesota in Minneapolis studied 22 507 postmenopausal women who had no history of cancer or heart disease and who took part in the Iowa women's health study. They presented their findings in an abstract at the annual meeting of the American Association for Cancer Research in Los Angeles last week (www.abstractsonline.com/viewer/searchAdvanced.asp, abstract 3400).

When the women enrolled in the study in 1992, they reported their use of aspirin and non-steroidal anti-inflammatory drugs and also their smoking history. The researchers did not question the women further but determined cancer incidence and mortality by annual linkage to the Iowa surveillance epidemiology and end results cancer registry and Iowa death certificates.

In the 12 years of follow-up there were 3487 cases of cancer and 3581 deaths, including 1193 that were due to cancer.

Compared with women who reported at baseline that they didn't use aspirin regularly, those who did report aspirin use had a 16% lower risk of developing cancer (relative risk 0.84 (confidence interval 0.77 to 0.9) and a 13% lower risk of dying from cancer (relative risk 0.87 (0.76 to 0.99)).

Women who were non-smokers or who had quit smoking had a lower incidence of cancer and death than current smokers, but the difference was not statistically significant.

Women who used aspirin regularly also had a lower risk of coronary heart disease and mortality.

Many previous studies have indicated that aspirin use, and sometimes use of non-steroidal anti-inflammatory drugs, reduces the risk of breast, ovarian, oesophageal, and colorectal cancer (BMJ 2003;327:572-3, doi: 10.1136/bmj.327.7415.572). Some studies, however, have not shown any benefit.

The women's health study, a randomised study conducted between 1992 and 2004 of nearly 40 000 healthy US women aged 45 years or older who were given 100 mg of aspirin or placebo every day and who were followed for 10 years did not show a benefit from aspirin (JAMA 2005;294:47-55). Aspirin use did not reduce the incidence of breast, colorectal, or lung cancer, and there was no reduction in cancer mortality except in the case of lung cancer.

Inflammation is thought to have a role in the development of cancer. Aspirin's inhibition of the inflammatory enzyme cyclo-oxygenase 2 is thought to be a key factor in the drug's protective effect (BMJ 2003;326:565, doi: 10.1136/bmj.326.7389.565).


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