People who took aspirin daily for five years or longer were less likely to die of cancer. The study that spawned this good news, published recently in the British journal The Lancet, probably cheered those already taking a baby aspirin a day to prevent a heart attack or stroke. But the inevitable wet blanket was thrown on the new finding by another British journal, the BMJ. Even low-dose aspirin has adverse effects that could be large enough to cancel any lifesaving benefit.

The reduction in cancer deaths came from the eight clinical trials that had randomly assigned participants to take low-dose aspirin or a placebo. These are the landmark trials that showed low-dose aspirin can lower the risk of heart attack and stroke; the trials that led an estimated 20 million Americans to take a baby aspirin daily. The medical records of the 25,570 participants became a gold mine for a team of researchers who wanted to see whether aspirin can also reduce the risk of colorectal cancer death. Peter M. Rothwell and colleagues searched these medical records and found fewer deaths from several different cancers among the study participants taking aspirin, compared to those taking the placebo.

Interestingly, all the cancers were of the solid tumor type. The reduction in deaths from esophageal, pancreatic, brain, and lung cancer showed up within five years of the study and reductions in stomach, colorectal, and prostate cancer showed up later. (Many participants continued to take aspirin long after the study was over.)

Rothwell and colleagues added that the benefit increased the longer the participants took aspirin. No perfect low-dose was identified because the participants were taking 75 mg (baby aspirin) or more. Unfortunately, there were not enough women in these clinical trials to be sure that the results apply to them. And this could explain why there was no reduction in breast cancer deaths.

Now for the wet blanket, which is about the bleeding risks of low-dose aspirin. Years ago I interviewed a research physician who said that no prevention trial has tested an aspirin dose so low that there were fewer serious bleeding incidents than those recorded in the placebo group. For my readers’ sake, I went off to find the lowest dose trial which turned out to be one that tested 100 mg aspirin—every other day—against a placebo. Sure enough, even at that extremely low dose, there were more serious bleeding incidents in the aspirin group than the placebo group. To complicate things further, I could find no low-dose aspirin study, including the one reported here, that separates fatal bleeds from those that are serious but not fatal.

This known increase in bleeding risk is the major concern expressed in the BMJ editorial that urged caution about the newly identified reduction in cancer deaths. The editorialists, Paul Moayyedi and Janusz A Jankowski, called attention to how modest this finding truly is. I’ve paraphrased their explanation:

There were 20 fewer cancer deaths among the 12,785 study participants who were on low-dose aspirin for almost six years, compared with those not taking aspirin (the 12,785 in the placebo group). But 100 more serious bleeding incidents occurred in the low-dose aspirin group, compared to the placebo group.

In short, “It is not clear that the benefits outweigh the risks, even when factoring in the cardioprotective effects of aspirin,” wrote the editorialists.

So what do we do now? Should millions of middle-aged and older people be on low-dose aspirin, as is currently recommended for the prevention of heart attack and stroke? The editorialists suggest waiting for the findings from an ongoing large trial that is evaluating the effectiveness of aspirin in preventing all causes of mortality. An analysis of this ongoing trial’s findings will be reported next year.

For more information:
There’s far more low-dose aspirin research on the question of heart disease prevention. So far, it shows the risk of bleeding is tiny but so is the benefit. Here’s how one team of researchers put it: “Aspirin for primary prevention is safe and worthwhile at a coronary risk of 1.5% a year or more, safe but of limited value at a coronary risk of 1% a year, and unsafe at a coronary risk of 0.5% a year. … We have to remember that aspirin, like all other drugs, is a poison.” (To follow this advice, you’d have to ask the prescribing doctor for your heart disease risk.) For more from the researchers who came to this conclusion, click here and scroll way down to Primary Prevention.

Maryann Napoli, Center for Medical Consumers ©