MUNICH – In a double blow to the current, widespread routine use of low-dose aspirin and fish oil supplements for primary cardiovascular prevention in patients with diabetes, neither treatment provided any net clinical benefit in the massive, long-term ASCEND study, investigators reported at the annual congress of the European Society of Cardiology.
And, in yet another bitter pill to swallow, low-dose aspirin failed to reduce the incidence of GI cancer or any other type of cancer, compared with placebo in the study. Earlier, nondefinitive meta-analyses of much smaller randomized trials had raised the possibility of a roughly 30% reduction in the incidence of colorectal cancer in long-time users, said Jane Armitage, MD, professor of clinical trials and epidemiology at the University of Oxford (England).
“We saw no suggestion of an anticancer effect emerging over time,” Dr. Armitage said. “We did see a significant reduction in the risk of vascular events but also an increase in major bleeding such that the absolute benefits from avoiding a serious vascular event were largely counterbalanced by increased risk of bleeding. And there was no subgroup in which we could clearly define that the benefit outweighs the risk,” she added in a video interview.
ASCEND (A Study of Cardiovascular Events in Diabetes) was a randomized, blinded trial in which 15,480 U.K. patients with diabetes and no known cardiovascular disease were placed on 100 mg/day of enteric-coated aspirin or placebo and 1 g/day of omega-3 fatty acids in capsule form or placebo in a 2 x 2 factorial design and followed prospectively for a mean of 7.4 years.
The study was undertaken because, even though the value of low-dose aspirin for secondary prevention is supported by strong evidence, the medication’s value for primary prevention in patients with diabetes has long been uncertain. American Diabetes Association guidelines give a Grade C recommendation to consideration of low-dose aspirin as a primary prevention strategy in patients with diabetes having a 10-year cardiovascular risk estimated at 10% or greater.
The primary efficacy endpoint in ASCEND was the occurrence of a first serious vascular event, defined as MI, stroke, transient ischemic attack, or death from any vascular cause other than intracranial hemorrhage. The rate was 8.5% in the aspirin group and 9.6% with placebo, for a statistically significant 12% relative risk reduction. However, the rate of the primary composite safety endpoint, comprising intracranial hemorrhage, GI bleeding, sight-threatening bleeding in the eye, or other bleeding serious enough to entail a trip to the hospital, was 4.1% in the aspirin group and 3.2% with placebo, a 29% increase in risk.
Aspirin reduced the absolute risk of a serious vascular event by 1.1%, compared with placebo, while boosting the risk of major bleeding by an absolute 0.9% – essentially a wash. The number needed to treat to avoid a serious vascular event was 91 patients, with 112 being the number needed to cause a major bleeding event. The risk of major bleeding rose with increasing baseline 5-year vascular event risk.
ASCEND provided no support for a recent report suggesting the benefit of low-dose aspirin for cardioprotection is largely confined to individuals weighing less than 70 kg (Lancet. 2018; 392:387-99); in fact, the opposite appeared to be true, according to Dr. Armitage.
The incidence of cancer of the GI tract was 2.0% in both study arms. The overall cancer rate was 11.6% in the aspirin arm and 11.5% with placebo. Additional follow-up focused on cancer is planned for 5 and 10 years after the end of ASCEND in order to examine the possibility of a delayed anticancer effect, she added.
Dr. Armitage said one reason aspirin may have failed to show a significant net benefit was the high rate of background cardioprotective medication usage, especially statins and antihypertensive drugs.
“I think if your diabetes is well managed and you’ve got your other risk factors under control, you have to consider very carefully whether or not, for you, the benefits of aspirin outweigh the risks,” she concluded.