Use of Aspirin as a Chemopreventive Strategy Is a ‘Close Call’

BETHESDA, Md--"Will an aspirin a day keep the oncologist away?" John Baron, MD, PhD, asked at a colon cancer prevention workshop held in conjunction with the American Society of Preventive Oncology (ASPO) annual meeting. "Absolute benefits and absolute risks are small," he said, "which means it’s a close call."

The good news, Dr. Baron said, is that several studies have shown that regular aspirin use (ie, 16 to 24 tablets per month) cuts the relative risk of colon cancer by about half in most population groups. On the other hand, this usage must continue for decades in order to reap any measurable benefit.

"So we have to consider other effects of aspirin before deciding whether to prescribe it as a chemopreventive," said Dr. Baron, professor of medicine and community family medicine, Dartmouth Medical School.

Reduction in Nonfatal MIs

Best known of these other beneficial effects is the association between aspirin use and a reduced risk of nonfatal heart attacks. For every 1,000 months of aspirin use, about four acute myocardial infarctions (MIs) are prevented, Dr. Baron said. However, there is virtually no reduction in the risk of vascular death or death from any cause with regular aspirin use.

Aspirin does have some cardiovascular risks--an increase in stroke (in primary prevention)--as well as gastric effects. "A single analysis should add up the costs, risks, and benefits, and weight their importance," Dr. Baron said. "These different factors have different importance. Is a nonfatal MI ‘worse’ that a nonfatal stroke?"

There is a temptation to make prevention efforts with aspirin more effective by targeting high-risk groups such as male patients with high blood pressure and high cholesterol who might have atherosclerosis. But, he said, there is "no consistent pattern of increased relative benefit in higher-risk individuals."

In a primary prevention setting, aspirin’s effect is very modest, Dr. Baron said. One has to wait longer for the effect of aspirin than for other available agents. With cholesterol-lowering agents, such as pravastatin (Pravachol), for example, reduced mortality appears soon after randomization, he said.

"I agree that aspirin is oversold in a primary prevention setting and might be detrimental overall (due to the increased risk of stroke in those over 75 years of age)," he said. "It’s a close call without further study of the NSAIDs."