LONDON — Evidence supporting the daily use of aspirin to help prevent and possibly treat cancer was published Tuesday in a collection of three papers — two in The Lancet and one in Lancet Oncology.
Previous studies have established that daily aspirin reduces the long-term risk of death due to cancer (Lancet 2007, 2010, 2011). However, the short-term effects were less certain, especially in women, as was how the risk/benefit of aspirin changes over time. In the first paper (The Lancet), lead author Peter Rothwell, professor at the University of Oxford and John Radcliffe Hospital, studied individual patient data from 51 randomized trials of daily aspirin versus no aspirin to prevent such vascular events as heart attacks.
They found that aspirin reduced the risk of a cancer death by 15%, compared with control groups. This improved to a 37% reduction risk of a cancer death for those on aspirin from five years and onwards. The reduction in cancer deaths on aspirin resulted in a 12% reduction in nonvascular deaths overall during the trials. In these trials of primary prevention, the reduction in nonvascular deaths accounted for almost all (91%) of the deaths prevented. Daily low-dose aspirin reduced cancer incidence by around a quarter from three years and onwards, with similar reductions in men (23%) and women (25%).
Although the reduced risk of major vascular events in these trials was initially offset by an increased risk of major bleeding, both these effects diminished over time, leaving only the reduced risk of cancer from 3 years and onwards (an absolute reduction of 3 cases per 1,000 patients per year, 12-per-1,000 control versus 9-per-1,000 in aspirin groups). The authors also found that case-fatality from major extracranial bleeds also was two-thirds lower on aspirin versus control groups.
"Alongside the previously reported reduction by aspirin of the long-term risk of cancer death, the short-term reductions in cancer incidence and mortality and the decrease in risk of major extracranial bleeds with extended use, and their low case-fatality, add to the case for daily aspirin in prevention of cancer," Rothwell said. "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."
A second article in The Lancet reported the effect of aspirin on cancer metastasis (i.e., how cancer grows/spreads). In this study, the authors collected new data on metastases of cancers that were diagnosed during all five large randomized trials of daily aspirin (75mg or more daily) versus control for the prevention of vascular events in the United Kingdom.
They found that, with a mean follow-up of 6.5 years, allocation to aspirin reduced risk of cancer with distant metastasis by 36%, risk of adencarcioma (common solid cancers including colon, lung, and prostate cancers) by 46%, and of other solid cancers (e.g. bladder, kidney) by 18%. These reductions were due mainly to a reduction by almost half in the proportion of adenocarcinomas that had metastatic disease.
The third study, published in The Lancet Oncology, also looked at aspirin's affect on metastases, this time using a systematic review of observational versus randomized trials. They found that observational studies showed a 38% reduced risk of colorectal cancer, matching well to the 42% reduction shown by randomized trials. Similar matches in risk were found for oesophageal, gastric, biliary and breast cancers.