A new study presents the latest meta-analysis from published observational studies that investigate whether long-term use of aspirin reduces the risk of developing gastrointestinal cancer. While the results show that aspirin can help prevent some cancers, some experts question how useful this association study is, especially when recent randomized clinical trials have come to very different conclusions.
The use of aspirin as a preventative medicine emerged in the late 20th century. First thought to reduce the risk of heart attack and stroke, it has recently been floated as a cancer prevention compound. However, evidence of the benefits of daily aspirin use is inconsistent, and scientists are still debating whether the risks outweigh the benefits.
A new study, led by an Italian research team, offers the largest meta-analysis conducted to date, focusing on a very specific relationship between long-term aspirin use and a reduction in the incidence of gastrointestinal cancer. The analysis collected data from 113 observational studies covering cancers such as colon, pancreas and liver.
The study defines regular aspirin use as at least one or two tablets per week, and concludes there is a dose-dependent relationship between aspirin use and a reduction in the risk of some cancers. In general, aspirin use is associated with a 27 percent reduction in colorectal cancer risk, a 36 percent reduction for gastric cancer, and a 22 percent reduction for pancreatic cancer. A higher dose, taken for a longer period of time, is associated with a greater risk reduction for cancer according to this study.
“We found that the risk of cancer was reduced with increasing doses; aspirin doses between 75 and 100 mg daily were associated with a 10% reduction in a person’s risk of cancer compared with people not taking aspirin; 325 mg daily doses were associated with a 35% reduction, and 500 mg daily doses were associated with a 50% reduction in risk, “said Cristina Bosetti, the author of the new study.” However, estimates of high-dose aspirin are based only on a few studies and must be interpreted with caution. “
Analysis shows the long-term use of aspirin provides the greatest benefit in reducing cancer risk, especially in relation to colorectal cancer. The greatest benefit is seen when aspirin is used for between five and ten years, however, the researchers noted several studies examining long-term (over ten years) use of aspirin.
“Compared to people who don’t take aspirin regularly, the risk of colon cancer decreases in ordinary aspirin users for up to ten years,” Bosetti added. “The risk is reduced by 4% after one year, 11% after three years, 19% after five years and 29% after ten years.”
All of these results may sound like good news, and offer the go-ahead for daily aspirin use, but it’s important to note that there are many other studies that suggest regular use of aspirin isn’t very beneficial if you are healthy.
Another meta-analysis of large observational studies published early last year looked at the relationship between daily aspirin use and cardiovascular events, but this analysis compares the potential benefits of aspirin against known dangers.
Pooling data from 13 studies, the analysis concluded there was a very small relationship between decreased cardiovascular events and aspirin use, however, aspirin use also increased the incidence of major bleeding events. The general conclusion of the analysis is that daily use of aspirin may be more dangerous than good, especially if someone is healthy and not at high risk of cardiovascular disease.
The majority of this study relies on observational research, which leads to a correlation between regular aspirin use and disease incidence. The gold standard for identifying causal relationships stems from randomized clinical trials, and one of the largest conducted on the subject to date reveals interesting main results in 2018.
Called ASPREE trial (ASPirin in the Reduction Program for the Elderly), more than 19,000 subjects over the age of 70 were followed for an average of five years. At the start of the trial, each healthy subject was randomly allocated to the placebo group or the low-dose (100mg) aspirin group.
Although many observational studies have linked aspirin use with lower cancer rates, the ASPREE trial was unexpected found no such correlation. A slight difference was seen between the placebo and aspirin groups, in almost every metric. In fact, the aspirin group surprisingly showed a slightly higher mortality rate for all cancer-related causes and deaths. Even stranger, the aspirin group in the ASPREE trial reported more deaths from colorectal cancer than the placebo group.
Andrew Chan, a professor of medicine from Harvard Medical School, said the discordant results found in the ASPREE clinical trial compared with this new meta-analysis might show aspirin only reduces the risk of developing cancer if it starts at a younger age.
“These results differ from the ASPREE trial, which found no association with lower cancer risk and even suggested the possibility of increasing cancer deaths,” Chan said in an email to New Atlas. “This may be due to the fact that ASPREE only checks for aspirin initiation in older populations. The differential effect of aspirin when starting later requires further investigation. “
In the end, Chan suggested low-dose aspirin might be a reasonable cancer risk reduction option if it starts between the ages of 50 and 60 years. However, he noted, this action should only be carried out after discussions with doctors about the risks and benefits.
Mark Nelson, from the University of Tasmania, worked on the ASPREE project and said the data from his team’s clinical trials were far more reliable than observational studies, even when the observational studies were collected in a meta-analysis.
“This is a meta-analysis of observational research and is therefore a residual destroyer,” Nelson said, commenting on the new research. “Large prospective clinical trials with decided cancer outcomes such as ASPREE are more stringent and therefore can be relied upon to provide evidence of harm or benefit.”
Nelson offers clear and concise answers when asked if there is a context for healthy people to use aspirin as a preventative agent.
“No,” he said.
Carlo La Vecchia, senior author on a new meta-analysis from the University of Milan, points out that although this research seems to show the beneficial effects of aspirin in the prevention of several cancers, there are many factors that need to be considered before a person starts taking medication. Every individual has their own set of subjective risk factors, meaning that there are no broad general recommendations that apply to everyone.
“Taking aspirin for the prevention of colon cancer, or other cancers, should only be done in consultation with a doctor, who can take into account the individual’s risk to that person,” La Vecchia said. “These include factors such as gender, age, family history of first-degree relatives with this disease, and other risk factors. People at high risk for this disease are likely to get the greatest benefit from aspirin.”
This new study was published in a journal History of Oncology.
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