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Understanding Cancer Prevention Trials
    Updated: 08/30/2001
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Cancer Prevention

There are two types of prevention clinical trials that study ways of reducing the risk of getting cancer:

  • Action studies (doing something)
These focus on finding out whether actions people take, such as exercising more or quitting smoking, can prevent cancer.
  • Agent studies (taking something)
These studies (also called chemoprevention studies) focus on examining whether taking certain medicines, vitamins, minerals or food supplements (or a combination of them) can prevent cancer.
In chemoprevention trials, people take medicines, vitamins, minerals or other supplements that researchers believe may lower the risk of a certain type of cancer. Health professionals who conduct these studies want to learn:
  • How safe is it to take the medicine or supplement?
  • Does the medicine or supplement prevent cancer?

How do prevention trials work?

A cancer prevention clinical trial that involves people results from a long and careful research process. As with other types of trials, each phase answers different questions about the study agent, which can be a medicine, vitamin, mineral, food supplement, or a combination of these.

Phase I trials are the first step in testing a prevention agent in people. Researchers try to identify the best way to give the study agent (e.g., by mouth), the best dose, and find out if there are any harmful side effects.

Phase II trials focus on learning whether the agent has an effect in preventing cancer.

Phase III trials compare a promising new agent to the standard one or to no agent, using two groups of people:

  • The intervention group - This is the group taking the study agent.
  • The control group - This group takes one of the following:
    • a standard agent that's being compared with the study agent;
    • a look-alike pill that contains no active ingredient, called a placebo.

Note that the placebo is almost never used in treatment trials in the United States.

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