asprin image 214x140Taking aspirin daily may cut a woman’s risk of ovarian cancer by 20%, according to a study published February 6, 2014 in the Journal of the National Cancer Institute. This new research adds to the large number of studies conducted in recent years showing aspirin may help prevent certain types of cancers. 

Other studies have found that regular aspirin use may help prevent colorectal, esophageal, stomach, prostate, and breast cancers, as well as certain types of skin cancers – and it also may keep cancer from spreading once it has been diagnosed.

Although much research on the topic has been done, the evidence still isn’t clear enough to show that the potential benefits of regular aspirin use with respect to cancer prevention outweigh the possible harmful side effects. Regular aspirin use can cause serious health problems such as internal bleeding, which is why no public health organization, including the American Cancer Society, currently recommends taking aspirin solely to reduce cancer risk.

In this interview, American Cancer Society researcher, Eric J. Jacobs, Ph.D., provides insights into what the studies to date really show when it comes to aspirin and cancer prevention, and discusses what other research is still needed.

Q. Is there, at this point in time, definitive evidence that regular aspirin use may help prevent certain cancers? Eric Jacobs

A. Yes, there is now definitive evidence that long-term daily aspirin use, even at low doses, will lower risk of developing one type of cancer – colorectal cancer, probably by approximately 40%. However, this benefit is unlikely to “kick in” immediately. There appears to be a delay of several years between when aspirin use is started and when risk of developing colorectal cancer is reduced.

It is also important to realize that aspirin can have serious side effects, which may outweigh its favorable effects on colorectal cancer risk. Therefore the American Cancer Society does not recommend using aspirin specifically to prevent cancer. More evidence about other types of cancers is needed.

Q. Are there certain types of cancers for which the evidence is stronger?

A. Besides colorectal cancer, there is very strong evidence that aspirin use lowers risk of developing cancer of the esophagus, and fairly strong evidence that aspirin use lowers risk of developing stomach cancer. These two cancers are not among the most common in the U.S., but they are of some importance because they tend to be very hard to treat.

For other cancers, the evidence is less clear. Some studies suggest that aspirin users are at 10% to 20% lower risk of developing certain other cancers, including two of the most common, breast cancer and prostate cancer. The new study in the Journal of the National Cancer Institute adds to the evidence that aspirin might modestly lower risk of ovarian cancer. However, other studies have found no effect. None of these studies are randomized trials, the most reliable type of study, where people are randomly assigned to take either aspirin or a placebo pill.

Q. What other studies need to be done to clarify whether aspirin can play a role in cancer prevention? And is it that more studies are needed, or that different types of studies are necessary?

A. The best study would be a new randomized trial where tens of thousands of people would be randomly assigned to take aspirin or a placebo pill daily for at least 10 years. However, a large long-term study like this would be expensive, and no such study has yet been started.

Two types of ongoing studies will help clarify what cancers aspirin may help prevent, and how long aspirin needs to be taken before any effects on cancer become apparent. First, there are randomized trials designed to study the effects of aspirin on heart disease – information from these same studies could be analyzed to study its effects on cancer as well. However, these studies may not answer questions about long-term effects because they typically involve taking aspirin for only about 5 years. Second, there are high-quality “observational” studies that track large numbers of people for decades, asking for detailed information on aspirin use every few years. A good example is the American Cancer Society’s recently started Cancer Prevention Study 3 (CPS-3), which includes approximately 300,000 men and women who will be tracked for at least 20 years. Over time, data from CPS-3 and similar studies will help clarify the long-term effects of aspirin on a wide range of cancers and other diseases.

Q. Do you think the research on aspirin and cancer prevention is promising – or is it really too early to say?

A. Research on aspirin and cancer prevention is definitely promising. It now appears possible that, over the long term, the same daily low-dose aspirin that can help prevent heart attacks could also help lower risk of several cancers. At the same time, even low-dose aspirin is a real drug, with potentially serious side effects. These include increased risk of ulcers and stomach bleeding, which can occasionally be serious enough to require transfusions and even cause death. Currently, there is not enough evidence that the cancer prevention benefits of taking aspirin outweigh these serious risks, so taking aspirin specifically to prevent cancer cannot be recommended.

Q. How long might it be until there is a clear answer as to whether it would be beneficial to people to take aspirin to help prevent cancer?

A. The main questions at this point are what cancers, beyond colorectal cancer, does aspirin help prevent; how long does it take for effects to “kick in”; and how much should we take cancer into account when we make decisions about aspirin use. Current clinical guidelines [from the U.S. Preventative Services Taskforce] recommend aspirin use for people who do not have other health issues that make taking it inadvisable and are at high risk for a heart attack, which includes most people who have already had a heart attack. These guidelines do not at this time consider cancer in balancing the risks and benefits of taking aspirin regularly. I expect that sometime within the next 10 years, the effects of aspirin on cancer will become a part of the overall risk/benefit calculation used to decide who should take aspirin. Making well-informed decisions about aspirin use will save lives.

Q. What is the bottom line at this time when it comes to taking aspirin?

A. At this point, neither the American Cancer Society, nor any other health organization, recommends taking aspirin specifically to help prevent cancer. People who are wondering if they should take aspirin should talk to their own health care provider, who knows their individual medical history and is aware of other medications they may be using, and can take this into account when weighing the risks and benefits of aspirin use.