As the UK descends into hysteria around petrol and pasties, I have been reflecting for the last week on Peter Rothwell’s recent Lancet papers about cancer prevention and the role of aspirin. Basically, daily low-dose aspirin not only prevents development of new cancer, but also the spread of cancer. Aspirin is one of the oldest drugs in the drug cabinet of hospital wards and GP surgeries, but we continue to discover more about its roles in medicine. As new evidence appears on the horizon, the information and guidelines for practising doctors and their patients still continues to change. There are inevitably time delays in how quickly new information filters through healthcare settings and broader society, and how it is interpreted by both the patient and the doctor.

Aspirin has several different uses which are proven by large bodies of evidence, including as a painkiller, prevention of cardiovascular disease in people at risk (primary prevention) and people with known cardiovascular disease (secondary prevention) and now for prevention of cancer. I always love to refer back to the Hippocratic Oath, and so we have to weigh aspirin’s harms with these many benefits. The main harm with aspirin is bleeding, particularly people who have a tendency towards bleeding anyway, e.g. individuals with history of gastric ulcers.

Interestingly, as the new data is emerging about the long-term preventive effects on cancer, the use of aspirin for two other indications is in decline due to evidence of not that much good when weighed against the risk of bleeding. First, most doctors do not recommend low-dose aspirin for primary prevention of cardiovascular disease, largely due to available data from meta-analyses showing that it does not change mortality in diabetics or non-diabetics. Second, in patients with atrial fibrillation, a heart rhythm problem which increases risk of stroke, aspirin is no longer recommended, yet most guidelinesaround the world still include it. So while we can recommend aspirin for long-term cancer prevention, we may not be able to recommend it in healthy individuals for long-term stroke prevention.

Evidence-based medicine is following a moving target of diseases and treatments and so the evidence is also always changing, even for drugs as old as aspirin. So for newer drugs, you can begin to imagine how little we know. The challenge is to keep all people, both doctors and patients up-to-date with all available evidence and guidelines. However, we know that this is difficult, given that both doctors do not always follow guidelines and people do not generally like to take tablets. Notably, most news reports covering the “aspirin and cancer” story advised people to go and see their doctor before starting the drug. Fergus Walsh, of the BBC, quoted a notable academic, “Doctors were good at treating disease, but when it came to preventing ill-health then people had to make their own judgements”. I agree. I wonder whether people have as much chance of making the “right decision” themselves. And before you ask, I do not take an aspirin a day yet, but I did start cycling to work again this week. One preventive step at a time.

A great deal of General Practice is essentially about managing risk. Every time a patient walks through your consulting door you are basically thinking “what are the chances of this patient coming to harm from what they are about to tell me?” Some patients will fall into a category of “high risk” needing immediate or quick treatment. Others may have a degree of risk that necessitates either further investigations or monitoring. Or there may be low risk cases which can be assessed, reassured or treated. This is all supposed to happen within 10 minutes.

But how far should we go to convey that risk to our patients and what is the best way to do it? A recent scenario at my practice made me pause for thought. The cardiologists had advised us to have a discussion with a patient on the merits and risks of aspirin versus warfarin for their atrial fibrillation.

How could that conversation go?

“Right Mr X, the cardiologists have written to me and asked me to help you decide between warfarin or aspirin. They mention in the letter that the risk of you now having a stroke is about 6% per year, however aspirin reduces that risk by about 25% but with warfarin there is about a 45% risk reduction. However, the number needed to treat with warfarin is 37, but bear in mind that warfarin increases the annual absolute risk of major haemorrhage by 2%, so it’s up to you, which one would you prefer? ”

“umm…I’m sorry Doctor, I didn’t understand all of that”

“No neither did I”

So how should we explain risk to patients? The 2002 BMJ clinical review “Explaining risks: turning numerical data into meaningful pictures” by Edwards and colleagues is certainly worth a read. More recently, a study in the Annals of Family Medicine also tried to answer the question. The group surveyed 934 consecutive patients drawn from family practitioners’ waiting rooms in Auckland, New Zealand. Patients were asked to rate how much various modes of communicating the benefits of therapy, to their 5-year CVD risk score, would encourage them to take medication daily. The modes offered to them included: relative risk, absolute risk, odds, number needed to treat, and natural frequencies. The same information was presented in 2 pictorial forms (bar graphs and 10 × 10 people charts). Most patients (61.8%) preferred a doctor to give an opinion than to explain using either numbers or pictures. More than half also preferred a pictorial presentation to numbers; and of the numerical presentations patients found relative risk reduction most encouraging, with absolute risk reduction rated second overall and numbers needed to treat (NNT) the least likely to be persuasive to take their medication.

So should this mean to our practice? Remember EBM is the integration of the best clinical practice, personal expertise and individual patient preference. The latter component is dependent upon the patient fully understanding the risks and benefits of treatment so that a shared management plan can be reached. Having an idea of what those risks mean ourselves is the first step but finding the best way to convey it to our individual patients in as simplest way as possible is perhaps the bigger challenge.

At the European Society for Cardiology Congress this week, we learned about more situations where aspirin is unhelpful. Professor Gerry Fowkes and colleagues from Edinburgh looked at nearly 30000 men and women aged 50 to 80 years who had never had any cardiovascular disease, but had a low ankle-brachial pressure index, a marker of peripheral vascular disease. The ankle brachial index (ABI) is the ratio of the blood pressure in the arm to the blood pressure at the ankle, and is an indicator of subclinical atherosclerosis. The ABI predicts risk of major vascular events in healthy populations, independently of established cardiovascular risk factors, such as diabetes, smoking and cholesterol. The Edinburgh team recruited over 3000 people with low ABI from their population and randomised them to 100mg aspirin or placebo, with 8 years of follow-up.

There was no difference between aspirin and placebo whether we look at cardiovascular events or all cause mortality, and there were more major bleeds in the aspirin arm of the trial. Same bottom line as before: do not give aspirin to people before they have a vascular event.