How do we know if medicines affect cancer risk?

By Eric Jacobs, PhD

You may be wondering if you should start taking an aspirin every day, since you’ve heard that aspirin can reduce the risk of heart disease and cancer. Or maybe your cholesterol level is a little high but you’re concerned about taking a statin pill every day because you saw an Internet article that said lowering cholesterol by taking a statin might cause cancer.

Or recently, a study came out that suggested that using the over the counter pain reliever acetaminophen at least 4 times a week for 4 years, might increase risk of certain types of blood cancers.

Medications often have unexpected long-term effects, both good and bad, that are not fully known. We’d all like to understand the full range of risks and benefits of a drug before we take it. Or at least we’d like our doctors to understand them so they can help us make well-informed decisions. [more]

Understanding the risks and benefits of medications is the goal of pharmacoepidemiology, the study of the use and effects of medications in large groups of people. Because cancer is a serious disease we all want to prevent, understanding if medications might raise or lower risk of getting cancer is especially important.

How Pharmacoepidemiology is Done

Where can you find good information about large groups of people, the medications they used, and what happened to them afterwards? One place is the American Cancer Society’s Cancer Prevention Study II (CPS-II).

More than 1 million men and women were recruited into CPS-II by Society volunteers. These men and women filled out a single questionnaire in 1982 about a variety of medical and lifestyle factors, including the medications they used, and have been followed up for deaths from cancer and other causes ever since. In 1992, an especially dedicated subgroup of more than 180,000 CPS-II participants, called the CPS-II Nutrition Cohort, signed up to be more intensively studied. CPS-II Nutrition Cohort participants have completed a new questionnaire approximately every two years, reporting updated information on dietary, medical, and lifestyle factors. CPS-II Nutrition Cohort participants have been followed up not only for deaths from cancer, but also for new diagnoses of cancer.

Studying Aspirin

CPS-II made front page news 20 years ago when it was the first large study to report that death rates from colorectal cancer were lower among people who used aspirin frequently than among those who did not, a finding confirmed by many later studies.

Nevertheless, aspirin use isn’t currently recommended specifically for reducing risk of colorectal cancer because it can cause serious stomach bleeding — and the higher risk of bleeding may outweigh the benefit of lower risk of colorectal cancer.

Aspirin use is, however, recommended for many people at high risk of a heart attack or stroke. Research has shown that for these people, aspirin’s benefits for reducing risk of heart disease and strokes outweigh its risks for stomach bleeding. As a result, millions of people now take aspirin to lower their risk of having a heart attack or stroke.

Very recent research has suggested that aspirin, when taken daily over many years, may lower overall cancer death rates. American Cancer Society epidemiologists are now studying the more detailed information available from the CPS-II Nutrition Cohort to see if this finding holds true in this study, also. If CPS-II and other studies show that aspirin helps prevent other types of cancer in addition to colorectal cancer, or lowers the risk of dying from cancer, then cancer prevention could be added to the list of benefits factored into decisions about who should take aspirin.

Aspirin is only one of the medications being researched. For example, an analysis of CPS-II data published by Society epidemiologists in February reported that long-term use of cholesterol-lowering medications was not linked with higher risk of any of the 10 most common cancers in the US, confirming the safety of these drugs.


Continuing Discovery

And that recent study about acetaminophen and certain types of blood cancers? We know there have been similar findings from some, but not all, previous studies And there’s no evidence from the recent study that suggests if you use acetaminophen less often or for less time that you have a higher cancer risk. This tells us that we need additional high-quality studies to tell us for sure. In the meantime, it’s important to realize that all pain relievers can have serious side effects, and people who need to use them regularly should talk to their health care professionals about which medications are right for them.

New studies are beginning that will be used for pharmacoepidemiology research, as well as for research on many other factors that may cause or prevent cancer. Currently, the American Cancer Society is recruiting a large new study population of US men and women for the Cancer Prevention Study 3 (CPS-3).

The men and women in CPS-3, like those in CPS-II before them, are providing information on a range of medical and lifestyle factors, including detailed information on use of aspirin and other medications. They will be tracked for decades so that we can better understand what causes cancer and how to prevent it. (Visit to learn more.)


Dr. Jacobs is the strategic director for pharmacoepidemiology at the American Cancer Society.


2 thoughts on “How do we know if medicines affect cancer risk?

  1. Hello- thanks for your questions. Here are some answers that I hope you find helpful.

    Regarding antioxidants, here’s some info from
    The body seems to use certain nutrients in vegetables and fruits to protect against damage to tissues that happens constantly as a result of normal metabolism (oxidation). Because such damage is linked with increased cancer risk, the so-called antioxidant nutrients are thought to protect against cancer. Antioxidants include vitamin C, vitamin E, carotenoids, and many other phytochemicals (chemicals from plants). Studies suggest that people who eat more vegetables and fruits, which are rich sources of antioxidants, may have a lower risk for some types of cancer. Clinical studies of antioxidant supplements are currently under way but have not yet proven to reduce cancer risk from vitamin or mineral supplements (also see entries for: beta-carotene, lycopene, vitamin E, supplements). To reduce cancer risk, the best advice at present is to get your antioxidants through food sources rather than supplements.

    And here’s some info about cosmetics:

    Thanks for reading the blog, and for your questions.

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