To reach the CRC recommendation, the task force mainly considered CVD trials in which cancer was a secondary finding, because there were limited data specifically on the effects of aspirin on cancer. From 10 trials (N=103,787), the task force determined that the individuals who took aspirin had a slightly reduced risk for death compared with those who did not (relative risk [RR], 0.96).
The task force weighed the benefits and risks of taking aspirin for the primary prevention of both CVD and CRC. It found that the prophylaxis was beneficial for some patients, but not for others.
“Fortunately, the task force found that [for] 50- to 69-year-olds at increased risk for cardiovascular disease, taking aspirin can help prevent heart attacks and strokes as well as colorectal cancer,” said Douglas K. Owens, MD, MS, a former member of the task force who led the review.
Cancer and CVD are major causes of death in the United States. Myocardial infarction (MI) and stroke are responsible for 30% of all deaths, and CRC is the third most common cancer, causing an estimated 50,000 deaths in 2014.
Among 72,926 individuals studied in six trials, the cancer incidence was similar in both groups (RR, 0.98). In contrast, among 14,033 individuals in two CVD primary and two CVD secondary prevention trials, there was reduced long-term CRC mortality in those who took aspirin (RR, 0.67). Four other trials (N=69,535) found no effect of aspirin on CRC incidence, but pooled analyses of three other trials (N=47,464) showed a lower risk in individuals who took aspirin for 10 or more years.
Risk factors for GI bleeding from a low-dose aspirin regimen included older age, male sex, upper GI tract pain, GI ulcers, concurrent anticoagulation or nonsteroidal anti-inflammatory drug use, and uncontrolled hypertension.
How much benefit an individual obtains depends on his or her age and risk for CVD. Daily low-dose aspirin has the greatest overall benefit for individuals aged 50 to 59 years, who are at increased risk for MI or stroke, and are not at risk for internal bleeding. Patients taking low-dose aspirin should have a life expectancy of at least 10 years, because it takes 10 years before benefits of the regimen will be seen, the task force added. It recommends aspirin initiation for this group. This is also the group most likely to benefit from low-dose aspirin to prevent CRC.
Individuals aged 60 to 69 years with increased CVD risk can also benefit from taking aspirin; however, the overall benefit in this group is lower, as is the benefit of taking aspirin to reduce CRC. Therefore, the decision to take aspirin must be based on the patient’s risks for CVD and hemorrhage, overall health, and personal values and preferences.
The task force concluded that the current evidence is insufficient to recommend aspirin use in people younger than 50 or older than 70 years. The evidence is insufficient for seniors because of the relationship between GI bleeds and age, the task force said. “The complexity of risk factors, medication use and concomitant illness make it difficult to assess the balance of benefits and harms of initiating aspirin use in this age group,” the task force wrote.
“Colorectal cancer prevention plays an important role in the overall health benefit of aspirin, but this benefit is not apparent until 10 years after aspirin therapy is started,” they noted, adding that patients need to take aspirin for at least five to 10 years to realize this potential benefit. Individuals with a shorter life expectancy, they wrote, would be less likely to benefit from the regimen.