Low dose aspirin: More evidence it can protect against colon cancer

A study appearing in the most recent Annals of Internal Medicine concludes that low- dose aspirin used every other day may reduce the risk of colorectal cancer in healthy women.

The report comes from a large study of nearly 40,000 women enrolled in the Women’s Health Study, a landmark trial that started in about in 1994, when researchers randomly assigned women aged 45 years or older to take either 100 mg of aspirin or placebo every other day for a period of about 10 years.

After the first ten years of the study, rates of colorectal cancer were the same in women who had taken aspirin and those who had taken placebo, leading some to conclude that the dose was too low to prevent colorectal cancer.  Women taking aspirin did, however,  have increased rates of gastrointestinal bleeding and peptic ulcers.  Now, however,  participants have been followed for a total of 18 years, including 8 years after aspirin use was stopped The new report shows that during the last 8 years of the study, the rate of colorectal cancer was about 40% lower in women who had originally been randomly assigned to take aspirin.

We asked Eric J. Jacobs, PhD, who himself has studied the association between aspirin use and cancer risk, for his reaction to the new study. 

“Studies conducted over about the last 20 years have provided convincing evidence that aspirin use lowers risk of developing colorectal cancer. Combined analyses of smaller trials of daily aspirin use published in the Lancet in 2010 suggested that regular use of even low-dose aspirin, such as the 81 mg aspirin tablet commonly used for heart disease prevention, lowers risk of colorectal cancer but only after a delay of several years.

Eric  J. Jacobs. Ph.D.

“The new results from the Women’s Health Study provide important evidence confirming that low-dose aspirin use does indeed lower risk of colorectal cancer, but that this benefit does not kick in until about 10 years after the start of regular use.

“It is important to remember that aspirin is a real drug with real side effects, including sometimes causing serious, even occasionally fatal, stomach bleeding, even at low doses.

“Aspirin use is recommended for most people who have had a heart attack, and has some benefits for colorectal cancer as well, but at this point the American Cancer Society does not recommend that people use aspirin specifically to prevent cancer.

“People who are uncertain about whether they should be using aspirin should talk to their health care provider who knows their personal medical history and can help weigh their individual risks and benefits.”

But unlike many cancers, colorectal cancer is largely preventable, thanks to screening. It usually takes 10 to 15 years for polyps to develop into colorectal cancer.  Most polyps can be found and removed before they have the chance to turn into cancer. Even if a polyp has already turned into cancer, finding it early, when it is highly curable, can save lives, which is why the American Cancer Society recommends colorectal cancer screening for all women and men 50 or older.

For more information, see “Can colorectal cancer be prevented?” on cancer.org.