What is chemoprevention?

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science.

This page was updated on February 28, 2022.

Chemoprevention drugs are different from chemotherapy drugs. Chemotherapy uses medicines to kill cancer, while chemoprevention uses medicines, vitamins or other substances to try to prevent cancer. Chemoprevention drugs are typically not used to treat existing cancers—only to try to prevent cancer from recurring or developing in the first place.

Doctors sometimes recommend chemoprevention if you face a particularly high risk of developing cancer in the future. To fall into this high-risk category, you may have:

  • Inherited cancer syndrome
  • Strong family history of cancer
  • Precancerous condition

Certain lifestyle factors may also put you at high risk, such as smoking, which raises the risk for lung cancer (and many other cancers).

Types of chemoprevention

Selective estrogen receptor modulators (SERMs): If you face a high risk of developing breast cancer, these drugs may be prescribed as prevention methods. SERMs such as tamoxifen and raloxifene mimic or block the effect of estrogen in different parts of the body.

Tamoxifen is prescribed to:

Tamoxifen may cause side effects and complications, including:

  • Hot flashes
  • Endometrial cancer
  • Blood clots
  • Cataracts
  • Stroke

Younger women (under 50) at high risk of breast cancer are often the best candidates for tamoxifen, as the risk of complications from this drug is elevated for older women.

Raloxifene is prescribed to reduce breast cancer risk in women who have already completed menopause. Unlike tamoxifen, raloxifene doesn’t seem to cause a higher risk of endometrial cancer. However, it may cause blood clots.

When taken every day for a maximum of five years, both drugs have been shown to lower the incidence of breast cancer by 50 percent among women at high risk of breast cancer, according to the National Cancer Institute (NCI). However, they’re prescribed sparingly due to side effects such as hot flashes and to the elevated risk of endometrial cancer that comes with tamoxifen.

Even after treatment is stopped, these drugs continue to reduce breast cancer risks for several years.

Finasteride and dutasteride: These drugs show promise in lowering the risk of prostate cancer. They belong to a class of medications called alpha-reductase inhibitors.

Finasteride and dutasteride decrease the production of male sex hormones and impede the bodily process of converting testosterone into dihydrotestosterone (DHT). Elevated DHT levels are thought to contribute to the development of prostate cancer.

The NCI has looked at several studies related to these drugs. In a clinical trial, finasteride seemed to reduce the risk of developing prostate cancer among healthy men older than 55. There were fewer instances of prostate cancer in the finasteride group than in the group that didn’t take finasteride. A trial of dutasteride in men with a high risk of prostate cancer showed similar benefits. However, it remains unclear whether men who take these drugs and still develop prostate cancer have a lower risk of death from the cancer.

Side effects of finasteride and dutasteride include:

  • Enlarged breasts
  • Erectile dysfunction
  • Lack of sexual desire

COX-2 inhibitors and other nonsteroidal anti-inflammatory drugs (NSAIDs): COX-2 inhibitors belong to a class of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs). Well-known NSAIDs include aspirin and ibuprofen.

COX-2 inhibitors such as celecoxib may have some value in preventing colon cancer. In studies, celecoxib has been shown to prevent benign tumors from reoccurring in the colon after removal and reduce the size and amount of colon and rectal polyps in people with familial adenomatous polyposis (FAP). However, these findings don’t prove that celecoxib also reduces overall colorectal cancer risk.

COX-2 inhibitors and other NSAIDs come with risks and complications, such as:

  • Congestive heart failure
  • Heart attack
  • Kidney problems
  • Bleeding in the stomach, brain or intestines

Aspirin is a different kind of NSAID that has also been studied as a potential method of chemoprevention. The evidence that aspirin use may reduce the risk of colorectal cancer is inconclusive. In April 2022, the U.S. Preventive Services Task Force updated its recommendations that some adults take aspirin to reduce their risk of both heart disease and colorectal cancer, saying that "the evidence is inadequate that low-dose aspirin use reduces (colorectal cancer) incidence or mortality."

Research related to aspirin and cancer has turned up mixed results, and the overall body of evidence suggests that aspirin isn’t an appropriate method to prevent most cancers, according to the NCI.

Is chemoprevention right for you?

Chemoprevention may not work for everyone. It’s best to ask your doctor about the risks and benefits of taking a chemoprevention approach. You may also:

  • Discuss major studies with your doctor. What were the results? Are you similar to the participants?
  • See whether there’s a clinical trial on chemoprevention that you may be qualified to join.
  • Find out whether you have other lifestyle factors that may affect your risk of cancer.

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