Newly published international papers are adding to growing research that Aspirin, commonly used now for people in danger of heart attack and stroke, may also help prevent and treat cancer.

Two papers in the Lancet and one paper in the Lancet Oncology, all published Tuesday, chronicle research suggesting daily use of acetylsalicylic acid (ASA, sold under the brand name Aspirin in Canada and other countries) can reduce the long-term risk of cancer death.

However, researchers from the U.K. and Italy, led by Prof. Peter Rothwell of the University of Oxford and John Radcliffe Hospital in England, stress that the short-term effects of daily use of the non-steroidal anti-inflammatory, as well as how risky or beneficial it may be over time, have yet to be determined.

Currently, in North America, medical practitioners are urged to put anyone who has had a heart attack or stroke on anti-platelet therapy (low-dose ASA, to prevent clots) because it can greatly reduce the risk of deadly recurrence.

The Lancet-published papers break down like this:

  • Article 1: The authors studied individual patient data from 51 randomized trials of daily Aspirin versus no Aspirin use to prevent heart attacks. They found Aspirin reduced the risk of a cancer death by 15 per cent compared with control subjects, and this improved to a 37 per cent reduced risk of a cancer death for patients taking the medication five years and longer. The reduction in cancer deaths for those taking Aspirin resulted in a 12 per cent reduction in deaths not related to the cardiovascular system. "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," the researcher wrote. 
  • Article 2: For the study on the effect of Aspirin on how cancer spreads (metastasis), new data was collected on metastases of cancers that were diagnosed during all five large randomized trials of daily Aspirin (75 milligrams or more daily), versus control for the prevention of cardio-related events in the U.K. They found that, with an average followup of 6.5 years, the use of Aspirin reduced the risk of cancer with "distant metastasis" by 36 per cent, cut the risk of colon, lung and prostate cancers by 46 per cent, and reduced the chance of bladder and kidney cancers by 18 per cent. Aspirin reduced the overall risk of fatal cancers in the trial populations by 35 per cent, but not the risk of blood and other fatal cancers. "These findings provide the first proof in humans that Aspirin prevents distant cancer metastasis," the researchers note, adding that metastasis had been prevented in previous studies involving animals.
  • Article 3: This paper reviewed the effect of Aspirin on metastatic cancer using a review of observational versus randomized trials. Researchers found observational studies showed a 38 per cent reduced risk of colorectal cancer, compared to 42 per cent in randomized trials. Similar matches in risk were found for esophageal, gastric, biliary and breast cancer, prompting the researchers to say, "Observational studies show that regular use of Aspirin reduces the long-term risk of several cancers and the risk of distant metastasis."

Aspirin prevented around one in 30 deaths from cancer among those who had a daily dose for about five years during a 20-year period.

In a commentary linked to the published research, scientists from Brigham and Women's Hospital, Harvard Medical School, in Boston said the studies make "a convincing case" that the cardiovascular-protection and anti-cancer benefits of Aspirin outweigh the harms that may include excess bleeding (hemorrhage), and "moves us another step closer to broadening recommendations for Aspirin use."

However, they warn, "these analyses do not account for less serious adverse effects on quality of life, such as less severe bleeding."

Although the Lancet-published studies received no specific funding, Rothwell has received honoraria for serving on advisory boards, clinical trial committees and giving talks from some pharmaceutical companies with an interest in anti-platelet agents, including Bayer, AstraZeneca,  Boehringer Ingelheim, Sanofi-BMS and Servier.