Can Aspirin Cut Cancer Deaths?

November 12, 2012

Can Aspirin Cut Cancer Deaths?

The Universities of Oxford, Edinburgh and Dundee, worked together with Kumamoto University, Japan, and the London School of Hygiene and Tropical Medicine, to produce this study, which was published in the medical journal The Lancet. It is stated by some researchers that research in animals shows an association between aspirin and a reduced risk of developing cancer. It is thought that aspirin may inhibit the occurrence of tumours, but the evidence produced so far has only been shown in mice. Evidence in humans has yet to be found conclusively.

Eight clinical trials were researched during this study which included more than 25,000 people. The study recorded daily aspirin use in the participants, during the follow up periods the number of cancer related deaths was recorded in comparison with non aspirin takers. Throughout the period of the study 674 people died from cancer.

The amounts of aspirin taken were much lower than that of a normal pain killing tablet, at 75mg it only contained about 25% of the aspirin in a standard pill.

How was it Reported?

The Daily Express took the rather spectacular view that “A daily dose of the ‘wonder drug’ aspirin is the simplest way to avoid dying from the most common cancers”. This was a very simplistic conclusion drawn from such a complex study.

A number of newspapers ran the story, all with varying amounts of accuracy. Some had derived that aspirin could ‘reduce the risk of developing cancer’ by up to 21%, yet the study only investigated actual cancer related deaths. That is, the risk of dying from cancer, not developing it. Although most of the papers did say that it was still early days and taking aspirin everyday has its own risk. Most papers did suggest that anyone wishing to take aspirin on a daily basis should talk to their GP first.

The Research

The research was undertaken because of a belief that rigorous scientific research into the area of ‘tumour or cancer prevention being an outcome of regular intakes of aspirin’ was required to provide more substantiated data on the matter. It was felt that evidence in humans was lacking, although animal experiments had produced promising results.

Some earlier observational studies appeared to show less association between aspirin and lower cancer incidence when the study was more rigorous. However less rigorous studies indicated a link. Random trials gave the same inconclusive evidence. Some trials indicated the risk of colorectal cancer was cut whereas others could find no links between lower cancer risk and aspirin usage.

The actual research consisted of a re-examination of previous studies. The earlier studies were generally used to assess the benefits of aspirin when dealing with angina or other heart related problems. Many of these trials were conducted over longer periods of time, sometimes years and because people died during the studies all of the information on the cause of death is included. This allows for percentages to be calculated for cancer related deaths. The researchers found clinical trials which compared any dose of aspirin with no aspirin. This included studies which compared aspirin to other drugs, such as warfarin.

Research databases were used to identify suitable studies. A study considered to be suitable must have followed people for an average of at least four years. By communicating with the original authors more information was given about the patients. Because of reliability issues with some of the data only analysis of fatal cancers was carried out.

This method of carrying out a study is considered valid because all of the previous studies being used stand up to scrutiny. Using previous studies in combination with other data is both cost effective and efficient and it allows for more links or associations to be identified.

There is a limit to the credibility that can be given to findings by this method though, because of the lack of uniformity of earlier studies. Some investigated patients for more years than others, and the fact that they were used for other reasons such as checking on vascular issues is also important to note. They were not designed to study the effects of aspirin and risk of cancer. Because of this many academics and health professionals will ask for further research before commenting on whether aspirin really can inhibit cancer.

However the research undertaken was conducted in a professional manner and when used with other evidence will be a very useful piece of work in the field of cancer prevention. The standards of researchers conducting the earlier studies are without doubt competent and professional as can be seen below:

  • The Thrombosis Prevention Trial (TPT, 5,085 people)

  • The British Doctors’ Aspirin Trial (BDAT, 5,139 people)

  • The UK Transient Ischaemic Attack Trial (UK-TIA, 2,435 people)

  • The Early Treatment Diabetic Retinopathy Study (ETDRS, 3,711 people)

  • The Swedish Angina Pectoris Aspirin Trial (SAPAT, 2,035 people)

  • Japanese Primary Prevention of Atherosclerosis with Aspirin for Diabetes (JPAD, 2,539 people)

  • Prevention of Progression of Arterial Disease and Diabetes (POPADAD, 1,276 people)

  • Aspirin for Asymptomatic Atherosclerosis (AAA, 3,310 people)

All of the studies recorded cause of death for every individual who died during the period of the study, but in the UK additional information was held on death certificates and some cancer databases.

The Findings

Throughout the studies of 25,530 participants 674 people died. By considering all of the eight reports together, findings showed that people taking aspirin had a 21% reduction in the risk of dying from cancer.

The study also found that there was no association between cancer related deaths and taking aspirin if only up to five years of follow up data was considered. However if the period under investigation was only more than five years of follow up then the reduced risk of cancer death was seen in regular aspirin takers.

The UK based studies which had longer term data on patients, up to 20 years, also confirmed lower cancer related death risks for people who took aspirin on a daily basis.

These findings prompted the researchers to say that ‘aspirin reduced the risk of death due to cancer by about 20% during the trials’. They go on to say that reduction to the risk of death by cancer is seen after five years of treatment and explain that because the original trials had a cross section of the populace the results should be applicable to most people. They also believe that there are no further benefits if more than 75mg a day of aspirin is taken.

Conclusion

As part of an ever growing body of evidence relating to cancer this well conducted study and its findings will be considered with other evidence whenever further research into cancer and cancer related deaths are conducted. However when considered in isolation the evidence does not permit the recommendation that aspirin should be taken daily to reduce the risk of cancer death. Long-term aspirin usage is known to cause internal bleeding in some people, particularly in older people and it is not clear if different groups of people may experience differing levels of benefit.

The results produced from the study actually came from studies which were not addressing the issue of cancer related deaths; most of the studies were related to vascular conditions. This means that the results although useful may not stand up to vigorous examination. Further research looking at the effect of aspirin on cancer is required. Future study may be widened to consider all cases of cancer, not just deaths.

The study was large; however certain types of cancer were not reported very often. This low incidence of cases adds to the difficulty of understanding the extent to which aspirin is effective in reducing the risks of dying of different types of cancer. Again further clinical trials or prospective studies are required before conclusive evidence is produced.

Because aspirin is known to be a cause of internal bleeding, the elderly being particularly at risk, it is certainly premature to advise everyone that taking aspirin everyday is a good idea. However if the GP has discovered other areas of risk in an individual then it may be prudent to consider that the benefits do outweigh the risks. This should not be taken to mean that this is the case for everyone, although it is known that people with heart conditions routinely take aspirin because of its benefits.

The researchers did discover that there did not appear to be any greater benefits achieved by taking more than 75mg a day, being only 25% of the over the counter aspirin sold as a painkiller reduces risks. However, the study does not put forward the evidence required for aspirin to be recommended to everyone.

The authors call for further research in the area of breast cancer or any other gynaecological cancers because the original studies did not include enough females for a meaningful assessment to be made.

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