According to the results of a study published in the New England Journal of Medicine, regular, long-term aspirin use reduces the risk of colorectal cancers that overexpress the COX-2 enzyme.
Colorectal cancer is the second leading cause of cancer-related deaths in the United States, highlighting the importance of finding effective approaches to colorectal cancer prevention.
Several studies have reported that regular aspirin use reduces the risk of colorectal cancer, but the biological basis for this protective effect has been uncertain. Researchers have speculated that aspirin’s inhibition of COX-2-an enzyme involved in inflammation-may explain at least some of the protection against colorectal cancer.
The extent to which colorectal cancers overexpress COX-2 varies. If aspirin’s effects on colorectal cancer are mediated primarily through inhibition of COX-2, aspirin may reduce the risk of only those cancers that overexpress COX-2.
To explore whether the effect of aspirin on colorectal cancer risk varies by COX-2 expression, researchers combined information from two large studies-the Nurses’ Health Study and the Health Professionals Follow-up Study.
- Of 636 colorectal cancers available for analysis, 423 (67%) had moderate or strong COX-2 expression.
- Regular aspirin use reduced the risk of COX2-overexpressing colorectal cancer by 36%.
- Regular aspirin use had no effect on the risk of colorectal cancers with weak or absent COX-2 expression.
The researchers conclude, “Regular use of aspirin appears to reduce the risk of colorectal cancers that overexpress COX-2 but not the risk of colorectal cancers with weak or absent expression of COX-2.” Among individuals with a history of colorectal cancer, it may eventually be possible to use information about COX-2 status to guide the use of aspirin for prevention of cancer recurrence.
Because of the potential risks associated with regular aspirin use, the U.S. Preventive Services Task Force does not recommend the use of aspirin or other non-steroidal anti-inflammatory drugs for the prevention of colorectal cancer in individuals at average risk of the disease.
 U.S Preventive Services Task Force. Routine Aspirin or Nonsteroidal Anti-inflammatory drugs for the primary prevention of colorectal cancer: U.S. preventive services task force recommendation statement. Annals of Internal Medicine. 2007;146:361-364.