I covered the recent announcement of Peter Rothwell et al research on reduction of cancer with Aspirin.
Crabsallover highlights in red with comments in bold orange.
A new study suggests that taking low doses of aspirin for at least five years can reduce the risk of dying from cancer. This is promising news, but if people are considering taking aspirin on a regular basis, they need to weigh up the benefits and risks with the help of their GP.
What’s the new study and what did it find?
The new study, published in the Lancet, was led by Professor Peter Rothwellfrom the University of Oxford. He combined the results of eight different clinical trials where volunteers took aspirin every day for at least four years.
None of the trials specifically set out to look at cancer, but they all recorded cancer deaths. Together, they included over 25,000 patients, of whom 674 died from cancer.
The results showed that people who took at least 75 milligrams of aspirin (the same dose as in a ‘junior’ aspirin) every day had around a 20 per cent lower risk of dying from cancer.
crabsallover says 'Results from Peter Roswell et al. In eight eligible trials (25 570 patients, 674 cancer deaths), allocation to aspirin reduced death due to cancer (pooled odds ratio [OR] 0·79, 95% CI 0·68–0·92, p=0·003).
crabsallover has read elsewhere that the pooled odds ratio of 0.79 or 1-0.79 = 21%. That's where the 20% figure comes from.
crabsallover assumes (correct me if I'm wrong) the probability p=0.003 means that the risk of this result arising by chance is 0.003%.'
To put this into perspective, if 100,000 people take aspirin every day for at least five years, around 56 cancer deaths will be avoided.
crabsallover says 'the 20% reduction is a relative figure, the 56 cancer deaths avoided per 100,000 people taking daily aspirin is the absolute figure. How did Cancer Research UK come up with the absolute figure? I assume the maths is like this:
- 56/100,000 = 0.05%. This seems a low %.
- In the developed world, the lifetime risk of cancer is
- about 40%
- (ref. 1 from Peter Roswell et al)
Rothwell found that it took at least five years for the drug’s benefits to become clear, possibly even longer for some cancers. If people took aspirin for more than five years, their odds of dying from cancer fell by around a third (34 per cent). And in the three trials that followed up their recruits for 20 years, the longer people stayed on aspirin, the greater the benefits they experienced.
Aspirin had a particularly dramatic effect on cancers that affect the digestive system, including the bowel, food pipe and stomach. It might also reduce the risk of dying from cancers of the lung, pancreas and brain.
The benefits of aspirin increased with age. For all the people in the trials combined, the drug reduced the risk of dying from cancer by 3.5 percentage points overall.
For people over the age of 65, it reduced the risk by 7 percentage points.
crabsallover says 'Results from Peter Roswell et al - Benefit was unrelated to aspirin dose (75 mg upwards), sex, or smoking, but increased with age—the absolute reduction in 20-year risk of cancer death reaching 7·08% (2·42–11·74) at age 65 years and older.
How does this fit with what we knew?
These latest results build upon a large amount of research on aspirin and cancer, which dates back several decades.
Aspirin works by blocking an enzyme called COX-2. (wikipedia - COX-2 or Cyclo-Oxygenase was discovered in 1991 by Daniel Simmons )
incidence or growth rate, or both, of several cancers in
animal models (refs: 4–6) mediated at least in part by inhibition
of the cyclo-oxygenase (COX) enzymes and reduced
production of prostaglandins and other inflammatory
mediators, but these findings might not be applicable to
humans. ref:Peter Roswell et al
The enzyme is involved in feelings of pain, which is why aspirin is an effective painkiller. It is also involved in inflammation, and as we’ve discussed before on this blog, persistent inflammation is a hallmark of cancer.
So it makes sense that aspirin could be a valuable weapon against cancer. And as we said the last time we wrote about this, large studies suggested that aspirin could potentially reduce the risk of several cancers, including bowel, breast and oesophageal cancers.
However, many of these studies suggested that you need large doses of aspirin –around 300mg per day or so – to reduce the risk of cancer. This is important, because aspirin has some harmful side effects including bleeding in the stomach and gut and the odds of suffering from these get worse the higher the dose.
However, in October, Prof Rothwell’s team at Oxford published a new study showing that even low doses of aspirin can reduce deaths from bowel cancer by around a quarter. Crabsallover blogged this research here.
It was an important result, especially because aspirin seemed to do best against tumours in the further reaches of the bowel.
Screening technologies such as Flexi-Scope are best at scanning the closer end of the bowel, so the two techniques – aspirin and screening – might work very well together to slash the number of people who develop and die from bowel cancer.
Prof Rothwell’s latest study expands on his previous work, to include other types of cancer.
Are there any concerns?
For a start, Prof Rothwell says that the results probably underestimate the benefits of aspirin for several reasons. Many of the people who were meant to be taking aspirin stopped taking part in the trials that Prof Rothwell looked at. The trials also stopped after a certain amount of time, so the true long-term benefits may be greater. Finally, the trials didn’t include enough women to tell us anything concrete about the effects of aspirin on breast or womb cancers.
Aspirin has other effects on health too, both positive and negative. It can lower the risk of heart disease and strokes but, as we said, it also increases the risk of bleeding from the gut and stomach. And when people stop taking it, their risk of stroke temporarily goes up.
There are some hints from Prof Rothwell’s study that the benefits outweigh the risks – they found that aspirin reduces the risk of dying at a given age by 8 per cent. However, this result was only just statistically significant, which means we cannot be sure if it’s down to chance.
Who funded the study?
The study didn’t receive any specific funding and it was “independent of any pharmaceutical company or commercial interest. Many of the authors have received fees from a wide range of pharmaceutical companies for talks and advice.
What does this mean?
The fact that low doses of aspirin can prevent people from dying from cancer is very promising. The drug is cheap and widely available, and low doses will minimise its risky side effects. In the past, Rothwell has suggested that middle-aged people should start taking aspirin from the age of 45.
However, it is still very important to consider the balance of benefits and risks. This is something that needs to be done on an individual basis, rather than making any broad sweeping advice for everyone. For some people, taking a daily aspirin might not be a good idea.
Prof Rothwell says that his team are gathering data from every available trial on aspirin and he’s due to publish his results in 2011. This should provide more answers about the balance of benefits and risks.
Cancer Research UK is watching the growing evidence in this area with keen interest, and we are also funding trials looking at whether aspirin can prevent cancer. For the moment, until things are a bit clearer, we’re recommending that people talk to their GPs if they’re considering taking aspirin on a regular basis.
Update: One of our leading scientists, Janusz Jankowski, who also works on aspirin and cancer, sounded a note of caution about the new results. You can read his full take on the study here.
Rothwell et al. 2010. Effect of daily aspirin on long-term risk of death due to cacner: analysis of individual patient data from randomised trials. Lancet DOI: 10.1016/S0140-6736(10)62110-1