Could aspirin help to prevent deaths from cancer, or even cancer itself?

British researchers have published the results of a study which shows that a small dose of aspirin daily could dramatically reduce incidences of cancer related death.

Published online and due to appear in the next issue of the Lancet, the study is the first of its kind, opening important new avenues of inquiry in the battle against all forms of cancer.

It was conducted by Professor Peter Rothwell, John Radcliffe Hospital, Oxford, and University of Oxford, UK, along with several other colleagues, including Professor Tom Meade from the London School of Hygiene and Tropical Medicine.

In October as separate study by professor Rothwell was published in the Lancet, which established that long-term low-dose aspirin (i.e. 75mg per day) reduced death rates from colorectal cancer by more than a third. The new research involves the study of deaths due to all cancers throughout and following randomised trials of daily aspirin compared to control, originally conducted to prevent vascular events.

All up 25, 570 patients were examined in eight eligible trials.

The researchers found that allocation to aspirin resulted in a 21 percent reduction of cancer-related death (based on 674 deaths). After five year follow-up death rates fell 34 percent for all cancers, with incidences of death from gastrointestinal cancers falling 54 percent.

Long term follow-up of patients following the trials (including 1634 cancer deaths), the researchers noted also that the 20-year risk of death from all solid cancers was lower in groups previously given aspiring compared to the control group, and an impressive 35 percent lower for gastrointestinal cancers.

Importantly, the study showed that the latent period before an effect on deaths was about 5 years for oesophageal, pancreatic, brain, and lung cancers, around a decade for stomach and colorectal cancers, with prostate cancer requiring the longest usage, approximately 15 years.

Looking at lung and oesophageal cancers, it appeared that the benefit was specific to adenocarcinomas, the cancers most common in non-smokers.

Aspirin was shown to reduce the 20-year risk of death from prostate cancer by some 10 percent, 30 percent for lung cancer, 40 percent for colorectal cancer and 60% for oesophageal cancer. Data was harder to assess in the case of pancreatic, stomach and brain cancers as there were relatively small numbers of deaths.

“This is an important epidemiological study on the benefits of aspirin for cancer prevention,” said Professor Bryan Williams, director of the Monash Institute of Medical Research, Monash University.

“The authors clearly demonstrate the remarkable protective effects of long term daily low dose aspirin against a variety of common cancers that likely have a common inflammatory component as part of their initiation process.”

Professor Williams noted that previous Monash studies (Silva AM et al J Biol Chem 282 10164-71, 2007) have showed that inhibition of cell’s ability to synthesise proteins is likely due in part to aspirin’s ability to block inflammatory processes.

“Epidemiological studies such as those underway in the Australian ASPREE study (P.I Prof John McNeil Monash University School of Public Health) will help address questions such as effects on breast and other women’s cancers posed by the current study.”

Professor Williams added that this latest study underscores the need for deeper study into the processes employed by salicylates, which is the active component of aspirin.

Importantly, the study's authors stressed that treatment with aspirin during the trials lasted on average between just 4-8 years, noting therefore that the effects on subsequent risk of deaths due to cancer may indeed be significantly greater with longer-term treatment, such as from between 50 and 70 years old.

Also interesting to note, the benefit was not affected by increased dose of aspirin, nor the patient’s sex or whether they smoked, but the absolute effect on 20-year risk of cancer death was shown to increase with age.

Professor Rothwell noted, however, that the aspirin’s greater effect on cancer death among the elderly is because of their already higher risk of death from cancer. In short, he said that if people are treated with 20 to 30 years of low-dose aspirin, it would be those starting treatment in their late 40s or 50s who would probably derive the greatest benefit.

"These findings provide the first proof in man that aspirin reduces deaths due to several common cancers. Benefit was consistent across the different trial populations, suggesting that the findings are likely to be generalizable,” said the authors of the report.

Rothwell cautioned, however, that "these results do not mean that all adults should immediately start taking aspirin, but they do demonstrate major new benefits that have not previously been factored into guideline recommendations,” adding that "previous guidelines have rightly cautioned that in healthy middle aged people the small risk of bleeding on aspirin partly offsets the benefit from prevention of strokes and heart attacks, but the reductions in deaths due to several common cancers will now alter this balance for many people."

In conclusion, the authors stated that taking aspirin daily for 5-10 years would likely reduce ‘all-cause mortality’ (including any fatal bleeds) over that period by about 10 percent.

As a result, there were further delayed reductions in cancer deaths, but no continuing excess risk of bleeding.

The researchers noted that the taking of aspirin would amount to a far more cost effective option to established initiatives such as screening for breast or prostate cancer, and that this may justify added costs related to the reduction of bleeding, including the co-prescription of proton-pump inhibitors, as well of course as the development of better derivatives of aspirin.

Nevertheless, while the study is indeed a fascinating revelation for cancer research, the researchers admit that more research is needed. For one thing, more needs to be done to study the effects of aspirin on the actual incidence of cancers, for both those that are less likely to be fatal as well as to see whether the latent period before aspirin becomes effective is shorter than that for death.

Further, they added that more trial data are required to determine the effect of aspirin on risk of breast and other cancers of women, while it is also necessary to follow-up beyond 20 years to discern any late rebounds in cancer deaths.

The researchers are currently working on a number of projects which they hope will offer answers to some, if not most of these questions by next year.

"Perhaps the most important finding for the longer-term is the proof of principle that cancers can be prevented by simple compounds like aspirin and that 'chemoprevention' is therefore a realistic goal for future research with other compounds,” concluded Professor Rothwell.