Three papers published in the Lancet and the Lancet Oncology show that aspirin, taken daily, may prevent cancer, and could even treat certain cancers. All three publications were from the same research group.
People that took daily aspirin had a 38% overall reduction of colorectal cancer and other gastrointestinal cancers compared to those who did not take aspirin.
Additionally, death rates from cancer in aspirin-takers were 15% lower, and rates of metastasis were about 35% lower.
One of the papers, from Peter M. Rothwell of the University of Oxford, John Radcliffe Hospital, in Oxford, UK and colleagues, adds to the case that aspirin could be helpful in cancer prevention in the short term. Previous research suggests that there is a long-term reduced risk of death from cancer associated with a daily aspirin pill.
The Rothwell study analyzed vascular-event randomized trials of daily aspirin compared to no aspirin. The analysis showed that there are short-term reductions in cancer incidence and deaths among people who took a daily low-dose aspirin.
Daily aspirin takers among 34 trials and over 69,000 participants had reduced cancer deaths (P = .008), especially after at least 5 years of taking aspirin. Among 6 trials focused on daily low-dose aspirin, the over-the-counter pill reduced cancer rates in women who took aspirin for at least 3 years (P = .0003), and also in men (P = .008).
These trials looked at primary vascular event prevention and found that the participants also had reduced risk of major vascular events, but an initial increased risk in major bleeding. The absolute reduction in cancer incidence was 3 cases per 1,000 participants per year—12 cancers per year in the pooled control groups compared to 9 in the aspirin groups.
The authors conclude that the pooled analysis "adds to the case for daily aspirin in prevention of cancer."
The second publication, from Annemijn M. Algra and Peter M. Rothwell, analyzed 51 case-control and cohort studies over the last 60 years that showed an association between aspirin use and risk or outcome of cancer. The results of the cohort studies parallel the randomized trial results.
The analysis of 17 studies, with a mean follow up of 6.5 years, suggests that aspirin is associated with a reduced risk of colorectal cancer (P < .0001), as well as esophageal, gastric, biliary, and breast cancers.
The final study found that aspirin reduced the risk of metastases among participants in 5 UK trials that aimed to assess the rate of cardiovascular events for aspirin vs placebo.
Participants that took regular aspirin had lower rates of distant metastasis or spread to regional lymph nodes, another finding consistent with previous randomized trials. The metastasis observation could also "explain the apparent early reduction in cancer incidence on aspirin" seen in the 6 primary prevention trials analyzed, according to the authors.
The authors suggest that because platelets play a role in metastasis to distant tissues, aspirin’s effect may be to change platelet dynamics. They propose that other antiplatelet drugs may also have a similar effect on metastasis.
"In view of the very low rates of vascular events in recent and ongoing trials of aspirin in primary prevention, prevention of cancer could become the main justification for aspirin use in this setting," state the authors.
In their comment on all 3 research studies, Nancy R. Cook, MD and Andrew T. Chan, MD, both of Brigham and Women’s Hospital, Harvard Medical School in Boston state that the research is an "impressive collection of data that moves us another step closer to broadening recommendations for aspirin use." They also postulate that any future utilization of aspirin to prevent vascular diseases must now also take into consideration the effect on cancer prevention.
However, the studies did not include 2 of the largest clinical studies that evaluated the effect of aspirin on cancer risk, the Physician Health Study and the Women's Health Initiative which combined, looked at over 60,000 people—neither demonstrated an effect on cancer risk, as highlighted by the comment.
Prospective, randomized trials are needed to assess the benefit-over-risk ratio of daily aspirin as well as long-term follow-ups of previous trials. Meanwhile, the current data, along with previous cohort, prospective, and mortality in case-control studies do point to aspirin as beneficial in staving off cancer. However, data on the mechanism of aspirin and the role of inflammation in preventing cancer is still lacking. Whether the current evidence is enough for the medical community to consider changing guidelines and to recommend aspirin as a preventive measure against cancer is yet to be seen.
1. Rothwell PM, Price JF, Fowkes FGR, et al. Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials. The Lancet. 2012 Mar 21. [Epub ahead of print]
2. Algra AM, Rothwell PM. Effects of regular aspirin on long-term cancer incidence and metastasis: a systematic comparison of evidence from observational studies versus randomised trials. The Lancet. 2012 Mar 21. [Epub ahead of print]
3. Rothwell PM, Wilson M, Price, et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. The Lancet. 2012 Mar 21. [Epub ahead of print]
4. Chan AT, Cook NR. Are we ready to recommend aspirin for cancer prevention? The Lancet. 2012 Mar 21. [Epub ahead of print]