From yesterdays PM, Radio 4: Professor Peter Elwood, epidemiologist at Cardiff University:

“I have always held that it is for the individual himself or herself to decide whether or not he or she would  take aspirin – they should be told the risks or the benefits and it should be the patients or subjects value that they put  on  on the possible outcomes . The way I see it myself is that  a heart attack or stroke cause disability,  have a very high risk of death, the downside is a bleed that at worst is going to lead to me being rushed into hospital for a blood transfusion but no sequalea, no after effects – I find it easy to value those, and to take aspirin. Some have exaggerated the risk of a bleed and one has to recognise that doctors practice defensive medicine but I think that the individual should make that decision.”

He’s talking about a study published over at the Lancet, where some esteemed people have analysed the deaths due to cancer,  in trials where people were being randomised to treatment with aspirin or not.

We already know that aspirin is of definite benefit for people at high risk of cardiovascular disease – namely those people who have already had a heart attack or stroke. But preventing the first event is rather different. Doctors used to recommend that people with diabetes  but who hadn’t previously had a heart attack or stroke  (but who nevertheless were at higher risk because of the diabetes)  took aspirin as a precaution. But then a study came along that said it made no difference to mortality, and u-turns were made.

For this is the problem with aspirin. It comes with side effects. Elwood as quoted on Radio 4 today is incorrect. People can die from the side effects of aspirin as used therapeutically. Bleeds into the brain or into the gut are the two most serious side effects. One may survive these. But they may be complicated by a pneumonia or a fractured hip and an individual may not recover. This means that we need to know what the all-cause mortality is – not just the effects of aspirin on the chosen parameter (eg, cancer mortality) but everything else too. There’s no point saving a cancer death if you precede yourself with another, potentially aspirin linked cause.

So, to  the Lancet study. We already know that aspirin is capable of preventing certain cancers. This study confirms that for people taking aspirin for 4 years or longer, there was a reduction in certain cancers. But the crunch is – when you look at the all-cause mortality, the results are not as impressive as the media reports have made out.

The graphs in the Lancet paper show that the reduction in cancer deaths achieved with aspirin is of the order of magnitude of a couple of percent off whatever the normal prevelance is. This is important when it comes to population measures to prevent cancer. But it has to be considered in terms of other population measures too – weight loss, for example, would reduce cancer rates, and so to would more exercise. Aspirin has side effects: for example, one study describing the use of aspirin for secondary prevention described it like this: ” aspirin treatment for a mean of 6.4 years resulted in an average absolute benefit of around 3 cardiovascular events prevented per 1000 women and 4 cardiovascular events prevented per 1000 men. This was offset by an additional 2.5 major bleeding events per 1000 women and 3 major bleeding events per 1000 men”.  Or try this, from the US Task Force on Preventive Medicine : “For 1000 patients with a 5% risk for coronary heart disease events over 5 years, aspirin would prevent 6 to 20 myocardial infarctions but would cause 0 to 2 hemorrhagic strokes and 2 to 4 major gastrointestinal bleeding events. For patients with a risk of 1% over 5 years, aspirin would prevent 1 to 4 myocardial infarctions but would cause 0 to 2 hemorrhagic strokes and 2 to 4 major gastrointestinal bleeding events.”

From the paper itself, I quote:

So aspirin isn’t a wonder drug, and the nuances of taking it are more complex than portrayed on the radio.  At the very heart of medicine is explanation of the possible courses  of interventions and assistance to make sense of the positives and negatives – and explain the uncertainties. The worst that can happen is not a little bleed of no consequence.  I’m keen to ensure that my patients have access to good unbiased information. There have been numerous researchers in the press over the last two days revealing that they are not taking aspirin as part of their endorsement of their studies. But they have that wrong, too. The studies that the Lancet have presented were not originally designed to assess whether or not cancer was reduced when taking aspirin. We still don’t know enough about the risks and benefits in a general, unselected population. The way forward is a better trial, not a presumption that doctor knows best.