Chemoprevention aims to help prevent cancer from developing or coming back. It can be effective for cancers such as breast and prostate cancer but has potentially severe side effects.

Cancer occurs when cells begin to grow in an uncontrolled, abnormal fashion. They might develop too quickly, be malformed, or live too long. Cancer prevention is primarily about stopping this process from happening or slowing it down.

Chemoprevention uses medications to help prevent the development of cancer. Doctors may recommend it to lower someone’s risk of a first cancer or cancer recurrence.

A hand with an IV tube for chemoprevention drugs holding a phone.-1Share on Pinterest
Santi Nuñez/Stocksy

According to the National Cancer Institute (NCI)Trusted Source, doctors may recommend chemoprevention for people with a high risk of certain cancers. There are several reasons why someone might be at a higher risk of developing cancer, including:

  • having a precancerous condition
  • a family history of cancer
  • some lifestyle factors, such as smoking

The American Cancer Society (ACS)Trusted Source highlights that this decision may vary among medical organizations.

For example, some may recommend chemoprevention for breast cancer in females over 35 years of age with a 5-year risk of 1.7% or more. However, other healthcare professionals may use different cutoffs when analyzing cancer risk.

Who is not suitable for chemoprevention

Doctors may not recommend chemoprevention if someone might have a higher risk of side effects from such treatment.

For example, the ACSTrusted Source suggests doctors may rule out the preventive drugs tamoxifen (Nolvadex, Soltamox) and raloxifene (Evista) in the following people:

  • people with a higher risk of serious blood clots
  • people who are pregnant or plan on becoming pregnant
  • anyone who is breastfeeding
  • people taking estrogen
  • people taking an aromatase inhibitor, a type of hormone therapy drug

According to the NCITrusted Source, research suggests the following chemoprevention drugs may have some effectiveness against cancer:

  • Selective estrogen receptor modulators (SERMs): These drugs include tamoxifen and raloxifene. They may lower the risk of breast cancer in people who are at very high risk.
  • Finasteride (Propecia): This drug may lower the risk of prostate cancer.
  • COX-2 inhibitors: These drugs may be able to help prevent colon and breast cancer.

The efficacy of chemoprevention may vary from case to case.

According to a 2020 review, research suggests SERMs may reduce the risk of some breast cancers by between 30% and 60%Trusted Source in people with a high risk.

The review’s authors also suggest that COX-2 selective inhibitors (COXIBs) and nonsteroidal anti-inflammatory drugs (NSAIDs) may also reduce the risk of colorectal cancers.

Older research in the review suggests that a daily 75 milligrams (mg) dose of the NSAID aspirin may lower the risk of such cancers by between 7% and 10%.

The NCI suggests that finasteride may lower the risk of prostate cancer. This effect may last up to 18 yearsTrusted Source after a 7-year treatment.

Anyone considering chemoprevention should consider the potential side effects of these medications.

For example, the NCITrusted Source notes that SERMs can cause hot flashes and that tamoxifen, specifically, may contribute to endometrial cancers.

The side effects of finasteride may includeTrusted Source:

COX inhibitors may causeTrusted Source:

The NCITrusted Source explains that doctors rarely recommend SERMs for chemoprevention due to the potential side effects. The side effects of COX inhibitors also mean that experts have not done much research on their use for preventing cancer.

Anyone with a higher risk of developing cancer may want to discuss chemoprevention with their doctor.

It may also be helpful to consider certain lifestyle choices for reducing the risk of developing cancer. For instance, the NCITrusted Source notes that the following choices may lower the risk of cancer:

How long does preventive chemo last?

How long chemoprevention lasts may depend on the individual and the type of drug. For example, chemoprevention using finasteride may be effective for several yearsTrusted Source.

People can speak with their doctor to learn how long chemoprevention may be effective for them.

Do you lose your hair with preventive chemo?

There is no evidence that chemoprevention typically causes hair loss. However, side effects of chemoprevention can range from hot flashesTrusted Source to kidney failure or strokeTrusted Source.

What is the difference between chemotherapy and chemoprevention?

Chemotherapy uses drugs that destroy or neutralize cancer cells that already exist. Chemoprevention uses drugs to prevent the development of these cells. Doctors may also recommend chemoprevention to stop a cancer from coming back.

Cancer resources

To discover more evidence-based information and resources for cancer, visit our dedicated hub.

Chemoprevention uses drugs to stop cancer cells from developing. This treatment can be useful for people who are at a high risk of cancer. It can also be useful for individuals who wish to prevent cancer from coming back.

Research suggests that chemoprevention may be effective against breast, prostate, and colorectal cancers. However, this treatment carries the risk of side effects, including hot flashes, low sex drive, and heart attacks.

People can speak with their doctor about chemoprevention if they have risk factors for cancer. A doctor can also recommend lifestyle changes to reduce the risk of cancer development.