Should You Take Aspirin to Prevent Pancreatic Cancer?

Perhaps you have seen some of the recent newspaper coverage of a National Cancer Institute-funded study[1] suggesting that long-term aspirin use may be associated with a decreased risk of pancreatic cancer. In this article, Public Citizen’s Health Research Group will review the study, compare it with earlier evidence and offer our recommendations.

Aspirin: Facts and usage

Aspirin, a drug that has been around since 1897,[2] is a common name for a chemical called acetylsalicylic acid or ASA (as it is still called in Canada and some other countries). It belongs to a group of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs).

Of NSAID medications, aspirin is the most well-known and most frequently used. When used as directed, aspirin is effective in relieving pain and reducing fever and inflammation. In addition, aspirin offers many cardiovascular health benefits. For example, when taken at the onset of a heart attack, aspirin is very effective at reducing the risk of death. Even when taken in low doses the drug also can lower the chances of future cardiovascular events among patients at risk for coronary artery disease, strokes and peripheral vascular disease (diseases of the arteries located outside the heart and brain).[3]

As a result, patients who have had a heart attack or stroke or who have multiple risk factors for cardiovascular disease are generally advised to take aspirin, unless they have conditions that make aspirin use too risky, such as bleeding in the stomach or intestines or a significant tendency for bleeding. Estimates from national survey data showed that approximately 43 million American adults took aspirin at least three times a week for more than three months in 2010,[4] a 57 percent increase in aspirin use since 2005.

The following side effects for aspirin can occur infrequently: nausea, abdominal pain or discomfort, inflammation of the stomach, ulcers of the stomach or small intestine, and even serious bleeding from ulcers.

Pancreatic cancer

Pancreatic cancer accounts for approximately 2.8 percent of all new cancer cases in the U.S.[5] Yet it currently ranks as the fourth-most-deadly form of cancer.[6] Risk factors for pancreatic cancer include cigarette smoking, family history, chronic inflammation of the pancreas, diabetes, obesity, a blood type other than O and Jewish or African-American ethnic origin.[7]

Early symptoms of pancreatic cancer are often nonspecific and attributed to benign conditions of the stomach or other abdominal organs. As a result, pancreatic cancer frequently goes undetected until conspicuous signs abruptly appear, by which time the malignancy may have reached an advanced stage. Overall, only 5 percent of individuals diagnosed with pancreatic cancer survive for five years or more after the diagnosis.

Results of the new study

The new study was published in July 2014 in the journal Cancer Epidemiology, Biomarkers & Prevention.[8] The researchers recruited 362 patients who were newly diagnosed with pancreatic cancer at 30 hospitals across Connecticut. They randomly selected an additional group of 690 participants without pancreatic cancer and compared them with the group that had developed the disease.

All study participants were interviewed to assess their health history, including when they started taking aspirin, how many years they had been taking it and whether the aspirin was taken in low doses (between 75 and 325 milligrams [mg] per day) or regular doses (325 to 1,200 mg every four to six hours for pain or inflammation).

The researchers found that routine aspirin use generally was associated with a reduced risk of pancreatic cancer. Particularly, participants who took low-dose aspirin on a continuous basis for six or fewer years had a 37 percent lower risk of pancreatic cancer, and those taking a low dose for more than 10 years had a 60 percent lower risk.

The study also found that the earlier routine intake of low-dose aspirin began, the lower the risk of developing pancreatic cancer: Participants who started three years before the study had a 48 percent lower risk, whereas those who started taking the drug 20 years before the study had a 61 percent lower risk.

Surprisingly, the researchers did not observe a similar trend among regular-dose aspirin users. Additionally, the researchers found that participants who stopped taking aspirin regularly within two years before the study had a threefold increase in their risk for pancreatic cancer, compared with those who continued aspirin use.

Comparison with a randomized clinical trial

The development of pancreatic cancer, as with any type of cancer, is a complex process that involves multiple risk factors that play out over many years, and it is difficult to know if or when an individual is going to develop cancer. Randomized controlled trials are much more effective at answering questions related to cancer and the effectiveness of preventive treatment than other types of studies, such as observational studies.

The new study was observational and retrospective: It examined the relationship between aspirin use and pancreatic cancer only after the cancer was diagnosed among the group with the disease, rather than following people who were given aspirin to see if they developed cancer. Therefore, it is unclear whether the findings were due to the difference in aspirin use or some other factor. In fact, the authors do not recommend that aspirin should be used daily to prevent pancreatic cancer.

More compelling data about aspirin intake and pancreatic cancer risk comes from a large, well-known randomized clinical trial called the Women’s Health Study (WHS). The WHS was conducted between September 1992 and March 2004[9] and was published in the July 6, 2005, issue of the Journal of the American Medical Association.

Researchers recruited approximately 40,000 American women at least 45 years old who had no previous history of cancer (including pancreatic cancer), cardiovascular disease or other major chronic illness. Half of the women were randomly assigned to an intervention group that received 100 mg of aspirin every other day, while the other half were assigned to a control group that received a placebo every other day. The subjects were followed for an average of 10 years. The trial measured whether subjects subsequently had a confirmed diagnosis of any new cancers, including pancreatic cancer.

The WHS found that aspirin use did not reduce the risk of developing pancreatic, breast, colorectal or any other type of cancer, except one. The exception was lung cancer, for which there was a trend toward reduction in risk. Also, with the exception of lung cancer, there was no reduction in cancer deaths overall or by type of cancer.

What You Can Do

The best available evidence, derived from the WHS, indicates that aspirin does not decrease the risk of pancreatic cancer. Therefore, while there are good reasons for many people to take aspirin, prevention of pancreatic cancer is not one of them.

Given the current lack of good evidence that aspirin use can prevent pancreatic cancer, you should not take aspirin on either a short- or long-term basis for this purpose. You also should know that clinical guidelines do not recommend taking aspirin specifically to prevent pancreatic or any other cancer.

If you are at high risk for pancreatic cancer, you should be under the care of a health care provider. Rather than trying to lower your cancer risk by using aspirin or any other unproven drug, it is better to work on reducing the risk factors associated with the disease by quitting smoking, eating a healthy diet and being physically active.

References

[1] Streicher SA, Yu H, Lu L, Kidd MS, Risch HA. Case-control study of aspirin use and risk of pancreatic cancer. Cancer Epidemiol Biomarkers Prev. 2014;23(7):1254-1263.

[2] Sneader, W. The discovery of aspirin: a reappraisal. BMJ: British Medical Journal 2000;321(7276): 1591-1591.

[3] Baigent C, Blackwell L, Collins R, Emberson J, et al. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet. 2009;373(9678):1849-1860.

[4] Zhou Y, Boudreau DM, Freedman AN. Trends in the use of aspirin and nonsteroidal anti-inflammatory drugs in the general U.S. population. 2014;(23):43-50. doi:10.1002/pds.

[5] Yeo TP, Lowenfels AB. Demographics and epidemiology of pancreatic cancer. Cancer J. 2012;18(6):477-484. doi:10.1097/PPO.0b013e3182756803.

[6] Siegel R, Ma J, Zou Z, Jemal A. Cancer Statistics, 2014. Ca Cancer J Clin. 2014;64(1):9-29. doi:10.3322/caac.21208.

[7] Yeo TP, Lowenfels AB. Demographics and epidemiology of pancreatic cancer. Cancer J. 2012;18(6):477-484. doi:10.1097/PPO.0b013e3182756803.

[8] Streicher SA, Yu H, Lu L, Kidd MS, Risch HA. Case-control study of aspirin use and risk of pancreatic cancer. Cancer Epidemiol Biomarkers Prev. 2014;23(7):1254-63. doi:10.1158/1055-9965.EPI-13-1284.

[9] Cook NR, Lee IM, Gaziano JM, et al. Low-dose aspirin in the primary prevention of cancer: the Women’s Health Study: a randomized controlled trial. JAMA 2005; 294: 47–55.