There are two types of prevention clinical trials that study ways of reducing the risk of getting cancer:
These focus on finding out whether actions people take, such as exercising more or quitting smoking, can prevent cancer.
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:
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:
Note that the placebo is almost never used in treatment trials in the United States.
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