Listen to the Cancer.Net Podcast: What is Chemoprevention?, adapted from this content.

Key Messages:

• Some substances can lower the risk of cancer or slow the development of cancer.
  
  
• Talk with your doctor about the benefits and risks (including side effects) of a chemopreventive agent before starting treatment.

Cancer chemoprevention is the use of natural, synthetic (made in a laboratory), or biologic (from a living source) substances to reverse, suppress, or prevent the development of cancer.

Cancer begins when cells become abnormal and grow uncontrollably. The transition from a healthy cell to a cancerous one usually takes many years and occurs in a series of steps influenced by genetic, dietary, and behavioral factors (such as smoking).

For some cancers, changes in normal cells can be recognized early when noninvasive, precancerous tumors develop. For example, colon polyps are growths in the lining of the colon or rectum. Most will not become cancerous, but sometimes, a polyp may develop into colon cancer. In the same way, the development of actinic keratosis (crusty bumps on the skin) can lead to skin cancer. However, not all cancers have early signs or symptoms.

Goals of chemoprevention

The goal of chemoprevention is to delay the development of cancer, not to treat existing cancer. Chemopreventive agents, alone or in combination with each other, can help slow down the processes that lead to invasive cancer. It is important to note that although cancer may be delayed with chemoprevention, it is possible that cancer could still develop in the future.

Some examples of chemoprevention include:

• Tamoxifen (Nolvadex), an estrogen blocker reduces the risk of invasive and noninvasive breast cancer; raloxifene (Evista) lowers the risk of breast cancer in women who have been through menopause. Learn more about drugs to lower breast cancer risk.
  
  
• Finasteride (Propecia, Proscar) and similar drugs that lower prostate cancer risk by reducing the amount of dihydrotestosterone (a male hormone) produced by the body. Learn more about ASCO's guideline on prostate cancer chemoprevention.
  
  
• Aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) to lower the risk of colon cancer for those at high risk of cancer.

Evaluating chemoprevention clinical trials

Clinical trials are research studies that test new treatment and prevention methods to find out if they are safe, effective, and better than the best known treatment (the current standard of care). All drugs or other substances that are thought to lower the risk of cancer are tested in clinical trials. When evaluating the results of chemoprevention clinical trials, it is important to look at the group of participants. Often, people with known, increased risks for cancer, such as those who smoke or have a family history of cancer, are studied, so the results of the study may not be applicable to everyone. For example, in the aspirin clinical trials, the participants were at higher than normal risk for developing colon cancer.

Risks and benefits of chemoprevention

Chemoprevention agents can help lower cancer risk or slow down the formation of cancer, but they can also have unwanted side effects. People with a higher risk of developing cancer (such as a previous cancer, inherited cancer syndrome, or a family history of cancer) may be willing to accept the possibility of side effects, whereas a person at average risk may not. For example, someone at increased risk for colorectal cancer may be willing to accept the risk of a medication's side effects to the heart in return for a lower risk of colorectal cancer. It is important to talk with your doctor about the risks and benefits of chemoprevention before starting treatment.

More Information

Clinical Trials

Risk Factors and Prevention

Last Updated: November 25, 2009