Can Aspirin Prevent Colon Cancer ? | The Body of Evidence

Can Aspirin Prevent Colon Cancer ?

New Guidelines from the US Preventative Services Task Force suggest adults should take a bay aspirin to prevent heart disease and now colon cancer as well. But, as usual, the devil is in the details.

I wrote about this issue in today's Montreal Gazette




Should everyone over 50 take a baby Aspirin once a day? If you have been watching the news carefully, you might think so. The U.S. Preventative Services Task Force just put out a draft statement recommending a baby Aspirin once a day to cut the risk of colon cancer. Quite apart from its cardiovascular benefit, the USPTF is suggesting that Aspirin can prevent cancer in those between the ages of 50 and 70.

There are, however, some caveats to this recommendation. First off, the age range is important. There is insufficient evidence for those under 50 or over 70 years old. In fact, individuals between 60 and 70 only got a Grade C recommendation in the USPSTF’s draft statement. People between 50 and 60 got only a Grade B recommendation rather than a Grade A.

The USPSTF is hedging its bets for a few reasons.

First, it’s important to note that the evidence supporting the use of Aspirin to prevent colon cancer is quite substantial. A 2012 meta-analysis of the data suggests that there is good quality evidence that daily Aspirin therapy reduces the risk of colon cancer. But not all the evidence is positive and two large trials, not included in the analysis, showed no benefit. In both, the Physician’s Health Study and the Woman’s Health Initiative, Aspirin did not prevent colon cancer.

Another important point that’s not usually mentioned is that many of the positive trials that showed a benefit were done in patients with a prior history of colon cancer. So it’s not clear if Aspirin is beneficial in the general population, which would obviously be at lower risk than these people. Finally, it appears that the benefit of Aspirin is seen only if you take high doses on a daily basis for about 10 years (raising questions about the utility of the baby Aspirin recommendation insofar as colon cancer is concerned).

Although there is some debate and inconsistency in the data, overall, there is probably some benefit to a daily Aspirin. Actually, there is probably a benefit to all anti-inflammatories and there is data showing reduced rates of colon cancer in patients taking drugs like Celebrex. But given that anti-inflammatories increase blood pressure and the risk of heart attack, there has been an understandable reluctance to recommend them to the general population.

Aspirin, of course, is beneficial in heart disease because it inhibits platelets and prevents the clotting that can clog the coronary arteries. In 1988, a trial confirmed that taking Aspirin when having a heart attack significantly reduces your chance of dying. Although data from the 1980s suggested benefit to daily Aspirin in otherwise healthy people, new evidence started emerging in 2009 that Aspirin was, in fact, not helpful.

The big change here is that in the intervening 20 years new medications to control blood pressure and cholesterol have gone a long way toward reducing cardiovascular risk. A 2012 meta-analysis of the old and new data found that Aspirin had a small benefit in preventing non-fatal heart attacks but that the benefit was cancelled out by an increased risk of bleeding.

So should everyone over 50 take a daily Aspirin? The answer is unequivocally no. The decision is a three-way balance of an individual’s cardiovascular risk, cancer risk and the risk of major bleeding. Let’s say you took 1,000 60-year-old men who were at moderate risk for heart disease and colon cancer. If you gave each of them an Aspirin every day for 10 years, you would get the following results: You would have 16 fewer non-fatal heart attacks, six fewer cases of colon cancer, no real difference in strokes and 16 more major bleeds. Overall, you would maybe have maybe six fewer deaths.

As with all medications, the decision to take Aspirin for prevention depends on weighing the risks against the benefits.

Christopher Labos is a Montreal doctor who writes about medicine and health issues.