Aspirin and its Chemopreventive Effect on Colorectal Cancer

Aspirin is a non-steroidal anti-inflammatory drug (NSAIDs) that is commonly used as a pain reliever, antipyretic (fever reducer), and preventative medication for cardiovascular illnesses. It is cost-effective, generic, and available over the counter. Aspirin has also been recommended as being beneficial in preventing the development of colorectal cancer (CRC). 

Aspirin has the ability to inhibit proliferation and allow apoptosis (cell-programmed death) of CRC cell lines. Approximately 10-20 billion aspirin tablets are consumed annually in the United States, making it one of the most commonly used medications in the world. The U.S. Preventive Services Task Force (USPSTF) has recommended that the use of aspirin can be of benefit in reducing the risk of CRC. Andrew Chan, M.D. wrote in Nature Reviews Cancer that the USPSTF recommendation is a ‘crucial step’ for cancer prevention.

The CAPP2 trial tested the effect of high-dose aspirin in carriers of the Lynch Syndrome. Also known as hereditary nonpolyposis CRC, Lynch syndrome is a hereditary condition that increases the risk of CRC and endometrial cancers. The trial concluded that 63% of patients who were given high-dose aspirin (600 mg/day) for a mean period of about 2 years saw a reduction in CRC development compared to the placebo group, over a period of about 5 years.  Comparably, the Cancer Prevention Program trial (CAPP3 trial) is a randomized trial that began recruitment in 2014 also targeted individuals with Lynch Syndrome but used varying doses of aspirin (100 mg, 300 mg, or 600 mg/day) for a duration of 2 years. Their follow-up period was 5-10 years later. Similarly, two large prospective cohort studies led by Dr. Chan at Harvard University established that the use of aspirin for 6 years or longer led to a 19% decreased risk of CRC. 

The data currently available on the benefits of aspirin were reviewed by Cuzick et al. who reiterated that the use of aspirin (75-325 mg/day) for greater than 5 years when started between the ages of 55-65 years, has shown benefit.

Although aspirin is chemopreventive for CRC, it is not without its adverse effects. Aspirin is an antiplatelet medication, which makes bleeding one of its most serious risk factors and therefore increases the risk for a hemorrhagic stroke by 32-36% and gastrointestinal bleeds by 30-70%. However, once the chemopreventive effects of aspirin are taken into consideration, the benefits outweigh the risk which is confirmed by an overall 4% reduction in CRC mortality. 

While there is an abundance of evidence as to the benefits of aspirin in the prevention of CRC, questions remain around the adequate dosage and duration of administration.