Is Aspirin the Magic Pill to Prevent Colorectal Cancer?

Colorectal cancer (CRC) is the second leading cause of death from cancer in the United States (US) and is most commonly diagnosed in adults between 65 and 74 years of age. In 2016, approximately 134,000 individuals were diagnosed with CRC, and nearly 50,000 died from the disease.1 If diagnosed early, the survival rate is greater than 90%, but it is less than 10% for later stage diagnoses.2 Commonly, patients present with rectal bleeding, weight loss, abdominal pain, diarrhea, or constipation. Additionally, patients may have signs of rectal disease or abdominal tenderness on physical examination. Due to chronic bleeding, patients may also have anemia.3

The development of the CRC disease process is a complex, step-wise process. It starts with the development of an abnormal growth pattern in the large bowel called “polyps” that can be benign or cancerous. As most polyps take over 7 years to transform from a medium sized polyp to cancer,4 screening can be particularly effective for this disease. The US Preventive Services Task Force (USPSTF) recommends screening for CRC in average-risk, asymptomatic adults between 50 to 75 years of age. There are multiple options for screening, but colonoscopy is considered the gold standard.

is there anything that can prevent CRC?

The human intestines harbor trillions of microbes that play fundamental roles in energy metabolism and immune function.5,6  Unfortunately, the reduced microbiota-accessible carbohydrate (MAC) intake that is characteristic of the Westernized diet has been shown to reduce gastrointestinal microbe diversity in mice studies. Since fiber is the most common source of microbiota-accessible carbohydrates or “microbe food” in the human diet, it is important to consume fruits, vegetables, lean meats, and seafood while staying away from processed foods that are high in saturated fats and largely devoid of fiber. Another option is administering probiotics to patients with microbial imbalance and inflammatory diseases in the intestines. Preliminary studies demonstrated that these steps reduce colitis, inflammation, and CRC.7 While pre- and probiotics have not yet been validated as prevention or treatment strategies, strong trends in literature speak to their potential therapeutic value.

Recent human evidence suggests aspirin as a possible preventive medication for CRC. A large study, published in 1988, showed an inverse association between aspirin use and risk of CRC.8 Subsequent studies of varying designs confirmed this association with both aspirin and commonly used over-the-counter pain medications called nonsteroidal anti-inflammatory drugs (NSAIDs).9 Published literature has shown that the reduction in risk ranges from 20% to 40%.10

Aspirin is an over-the-counter medication commonly used for prevention of cardiovascular diseases, stroke, fever, and pain control. It has pain-relieving and anti-inflammatory properties and inhibits the clumping of small cells called platelets in our blood vessels, which helps prevent stroke and cardiovascular diseases. It is absorbed in the stomach and upper intestine when taken by mouth. As with all drugs that affect platelets, there is a risk of bleeding and it also irritates the stomach wall. Many adverse effects of aspirin are dose-related and are rarely seen at low dosages. With all this evidence about the protective effects of aspirin, some important questions arise.

How does Aspirin prevent CRC?

Multiple mechanisms have been proposed and proved in animal models. Aspirin inhibits tumor cell multiplication, causes cancer cell death, and affects other markers of cancer growth.10 This is an area of ongoing research.

What is the ideal dose of Aspirin to prevent CRC?

It is still unclear. Medical studies have not provided precise estimates of the amount of aspirin needed to prevent CRC. Some evidence indicates baby aspirin, which is routinely recommended to prevent cardiovascular disease, or even alternate day low-dose aspirin may be effective. Higher doses are not routinely recommended because of side effects.11

How long do I have to take Aspirin to prevent CRC?

There is also conflicting evidence on how long aspirin must be taken to prevent CRC. The accepted range necessary to achieve substantial reductions in the risk of CRC varies from 3 to 10 years. All potential risks and benefits of prolonged aspirin use must be carefully weighed before recommending it for disease prevention.12 While there is evidence that aspirin is associated with a reduction in CRC, it is important to realize that this is not an alternative to colonoscopy. It can be an affordable, accessible, and safe preventive approach, but continuous aspirin consumption can have side effects, such as internal bleeding. You should talk with your care provider before taking aspirin for CRC prevention.

References
  1. Bibbins-Domingo K, Grossman DC, Curry SJ, et al. Screening for Colorectal Cancer. JAMA. 2016;315(23):2564. doi:10.1001/jama.2016.5989.
  2. Hamman MK, Kapinos KA. Colorectal Cancer Screening and State Health Insurance Mandates. Health Econ. 2016;25(2):178-191. doi:10.1002/hec.3132.
  3. Hamilton W, Round A, Sharp D, Peters TJ. Clinical features of colorectal cancer before diagnosis: A population-based case-control study. Br J Cancer. 2005;93(4):399-405. doi:10.1038/sj.bjc.6602714.
  4. Cappell MS. Pathophysiology, Clinical Presentation, and Management of Colon Cancer. Gastroenterol Clin North Am. 2008;37(1):1-24. doi:10.1016/j.gtc.2007.12.002.
  5. Hooper LV, Littman DR, Macpherson AJ. Interactions between the microbiota and the immune system. Science (New York, NY). 2012; 336:1268–1273.10.1126/science.1223490
  6. Karlsson F, Tremaroli V, Nielsen J, Backhed F. Assessing the human gut microbiota in metabolic diseases. Diabetes. 2013; 62:3341–3349.10.2337/db13-0844 [PubMed: 24065795]
  7. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol 2014;11:506e14.
  8. Kune GA, Kune S, Watson LF. Colorectal cancer risk, chronic illnesses, operations, and medications: case control results from the Melbourne Colorectal Cancer Study. Cancer Res. 1988;48(15):4399.
  9. Rostom A, DubéC, Lewin G, Tsertsvadze A, Barrowman N, Code C, Sampson M, Moher D, U.S. Preventive Services Task Force. Nonsteroidal anti-inflammatory drugs and cyclooxygenase-2 inhibitors for primary prevention of colorectal cancer: a systematic review prepared for the U.S. Preventive Services Task Force. Ann Intern Med.2007;146(5):376.
  10. Barnes CJ, Lee M. Chemoprevention of spontaneous intestinal adenomas in the adenomatous polyposis coli Min mouse model with aspirin. Gastroenterology. 1998;114(5):873.
  11. DubéC, Rostom A, Lewin G, Tsertsvadze A, Barrowman N, Code C, Sampson M, Moher D, U.S. Preventive Services Task Force. The use of aspirin for primary prevention of colorectal cancer: a systematic review prepared for the U.S. Preventive Services Task Force. Ann Intern Med. 2007;146(5):365.
  12. Chan AT, Giovannucci EL, Meyerhardt JA, Schernhammer ES, Curhan GC, Fuchs CS. Long-term use of aspirin and nonsteroidal anti-inflammatory drugs and risk of colorectal cancer. JAMA. 2005;294(8):914.

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