More evidence for aspirin in cancer prevention

Friday, March 23, 2012. Articles published this week in The Lancet and The Lancet Oncology add evidence to a benefit for aspirin in protecting against cancer and preventing metastasis in pre-existing disease.

Professor Peter M Rothwell of the University of Oxford and his colleagues conducted the research described in all three reports. In the first article, Dr Rothwell's team analyzed data from 51 clinical trials that compared the effects of daily aspirin to no aspirin on the risk of cardiovascular events. They observed a 15 percent lower risk of dying of cancer over the course of the trials for those who received daily aspirin, which improved to a 37 percent reduction for those who received aspirin for five years or more. Cancer incidence was reduced as well, resulting in a 23 percent decrease in men and a 25 percent lower risk in women.

In the second Lancet study, Dr Rothwell and his associates reviewed five large trials that sought to determine the effect of daily aspirin on the effects of vascular events. Among 17,285 participants, 1,101 cases of cancer were diagnosed during the trials, including 563 fatal cases. Over an average 6.5 year follow up period, those who received aspirin had a 36 percent lower risk of being diagnosed with cancer with distant metastases, mainly due to a reduction in the proportion of metastatic versus nonmetastatic adenocarcinoma. Aspirin also reduced the risk of dying of cancer among adenocarcinoma patients. The effects were independent of gender and age, and were additionally observed in association with a low-dose, slow-release aspirin designed to inhibit platelets while having little systemic bioavailability. "That aspirin prevents metastasis at least partly accounts for the reduced cancer mortality recently reported in trials of aspirin versus control in prevention of vascular events and suggests that aspirin will also be effective in treatment of some cancers," the authors write. "The lack of dependence of this effect of aspirin on its systemic bioavailability suggests that it is platelet-mediated. Other antiplatelet drugs might therefore have a similar effect on risk of metastasis and combining different drugs might increase benefit."

The review published in The Lancet Oncology analyzed case-control and cohort studies that compared the risk of cancer experienced by aspirin and nonaspirin users. "Long-term follow-up of randomized trials of aspirin in prevention of vascular events showed that daily aspirin reduced the incidence of colorectal cancer and several other cancers and reduced metastasis," the authors write. "However, statistical power was inadequate to establish effects on less common cancers and on cancers in women. Observational studies could provide this information if results can be shown to be reliable. We therefore compared effects of aspirin on risk and outcome of cancer in observational studies versus randomized trials."

The results of these observational studies indicate a 38 percent lower risk of colorectal cancer over a 20 year period in association with aspirin use, which is in agreement with the reduction found in clinical trials. Similar decreases were found for esophageal, stomach, breast and biliary cancers.

In a commentary published in The Lancet, Dr Andrew T Chan and Dr Nancy R Cook of Brigham and Women's Hospital and Harvard Medical School write that "Rothwell and colleagues' impressive collection of data moves us another step closer to broadening recommendations for aspirin use. Moreover, future evidence-based guidelines for aspirin prophylaxis can no longer consider the use of aspirin for the prevention of vascular disease in isolation from cancer prevention."