That hazard ratio “rules out the possibility of a major protective effect of aspirin but is compatible with a more modest lowering of risk of up to 17%,” Dr. McNeil and colleagues wrote.
The results are consistent with those of a recent meta-analysis including eight primary prevention trials, mainly in adults under 70 years of age. That analysis found a 17% reduction in nonfatal myocardial infarction risk, a 14% reduction in stroke risk, and a higher risk of serious bleeding for aspirin versus control groups.
Results of ASPREE have to be interpreted in light of event rates, which were much lower than the expected 22.4 events per 1,000 person-years, they added. The low event rate probably reflects both the relatively good health of the study subjects, and the declining rates of cardiovascular disease in recent years, they said.
“Because of these factors, the absolute benefit that results from any proportionally lower rate of cardiovascular disease may be less than the benefit observed in studies from previous decades and is less likely than it had been to outweigh the risk of adverse events from aspirin,” investigators said in their report.
Current guidelines state that the evidence is limited for use of aspirin as primary prevention of cardiovascular disease in the elderly. “Nevertheless, many millions of relatively healthy older persons in the United States and Australia take low-dose aspirin with the assumption that it will reduce the likelihood of future cardiovascular disease and stroke,” study authors said in a discussion of the results.
Excess deaths explored
There were also no significant differences between arms for the endpoints of death, dementia, or disability evaluated separately. However, the rate of death by any cause was numerically higher in the aspirin group versus the placebo group, at 12.7 and 11.1 events per 1,000 person-years, respectively (HR, 1.14; 95% CI, 1.01-1.29).
Cancer was the major contributor to the imbalance in deaths, ASPREE results show, at 1.6 excess deaths per 1,000 person-years. A total of 3.1% of patients in the aspirin group had cancer-related deaths, compared with 2.3% in the placebo arm of the trial (HR, 1.31; 95% CI, 1.10-1.56).
Mortality related to major hemorrhage contributed “only minimally” to the excess in deaths, investigators added in their report.
The finding of excess deaths in the aspirin arm of ASPREE contrasts with meta-analyses of previous prevention trials. According to investigators, those studies show a protective effect of aspirin on cancer-related death that is apparent after 4-5 years of continuous treatment.
Various cellular and molecular pathways relevant to cancer development, progression, and spread are influenced by aspirin, previous studies show.
“Questions may therefore arise about whether the biology of cancer differs among age groups with regard to the frequency of common molecular patterns, metastatic behavior, and treatment responses,” Dr. McNeil and coauthors wrote in their report.
Dr. McNeil reported nonfinancial support from Bayer received during the conduct of the study.
SOURCE: McNeil JJ et al. N Engl J Med. 2018 Sep 16.