Low doses of acetylsalicylic acid increase risk of gastrointestinal bleeding in a meta-analysis

Gastrointestinal lesions and complications of low-dose aspirin in the gastrointestinal tract

Low dose aspirin (ASA) use has been associated with a wide range of adverse side effects in the upper gastrointestinal (GI) tract, which range from troublesome symptoms without mucosal lesions to more serious toxicity, including ulcers, GI bleeding, perforation and even death. Upper GI symptoms in low dose ASA users are common but often careless or misinterpreted and they are not always related to the presence of mucosal injury. Usually, low dose ASA related ulcers are reasonably small and asymptomatic, and probably heal over a period of weeks to a few months. But, the real clinical problem occurs when the ulcer results in a GI complication (mostly bleeding). The estimated average excess risk of symptomatic or complicated ulcer related to low dose ASA is five cases per 1000 ASA users per year. Death is the worst outcome of GI complications in low dose ASA users, but data about this aspect are scarce. Current evidence indicates that low dose ASA can damage the lower GI tract also, but the real size of the problem is still unknown.

Aspirin in the chemoprevention of colorectal neoplasia: an overview

Considerable evidence supports the effectiveness of aspirin for chemoprevention of colorectal cancer (CRC) in addition to its well-established benefits in the prevention of vascular disease. Epidemiologic studies have consistently observed an inverse association between aspirin use and risk of CRC. A recent pooled analysis of a long-term posttrial follow-up of nearly 14,000 patients from four randomized, cardiovascular disease prevention trials showed that daily aspirin treatment for about five years was associated with a 34% reduction in 20-year CRC mortality. A separate metaanalysis of nearly 3,000 patients with a history of colorectal adenoma or cancer in four randomized adenoma prevention trials showed that aspirin reduced the occurrence of advanced adenomas by 28% and any adenoma by 17%. Aspirin has also been shown to be beneficial in a clinical trial of patients with Lynch syndrome, a hereditary CRC syndrome; in those treated with aspirin for at least two years, there was a 50% or more reduction in the risk of CRC commencing five years after randomization and after aspirin had been discontinued. A few observational studies have shown an increase in survival among patients with CRC who use aspirin. Taken together, these findings strengthen the case for consideration of long-term aspirin use in CRC prevention. Despite these compelling data, there is a lack of consensus about the balance of risks and benefits associated with long-term aspirin use, particularly in low-risk populations. The optimal dose to use for cancer prevention and the precise mechanism underlying aspirin's anticancer effect require further investigation.

Aspirin for the prevention of colorectal cancer

Over 600,000 people worldwide die of colorectal cancer (CRC) annually, highlighting the importance of developing effective prevention strategies. Among proposed chemopreventive interventions, aspirin is perhaps the agent with the strongest body of evidence that supports wider spread use to significantly reduce the population burden of CRC. Several epidemiological studies, four randomized controlled trials (RCTs) of colorectal polyp recurrence, and RCTs in patients with hereditary colorectal cancer syndromes, have shown that aspirin reduces incidence of colorectal neoplasia. Recently, in a pooled analysis of five cardiovascular-prevention RCTs linked to cancer outcomes, daily aspirin use at any dose reduced the risk of CRC by 24% and of CRC-associated mortality by 35% after a delay of 8-10 years. In an expanded meta-analysis of 8 cardiovascular-prevention RCTs, daily aspirin use at any dose was associated with a 21% lower risk of all cancer death, including CRC, with benefit only apparent after 5 years. In this review, we will summarize human studies of aspirin in CRC prevention as well as discuss the safety profile and mechanism of aspirin in CRC prevention.