How Do Researchers Design
Cancer Prevention Clinical Trials?
A cancer prevention clinical
trial that involves people results from a long and careful research
process. As with other types of trials, each step, or 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.
Doctors try to find the best way to give the study agent (for
example, by mouth), the best dose, and if there are any harmful
side effects.
- Phase II trials
focus on learning whether the agent has a biologic 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 either:
- 1. a standard
agent that's being compared with the study agent;
- 2. a look-alike
pill that contains no active ingredient, called a
placebo.
Because less is known about
possible risks and benefits in Phase I and II, these trials
usually include only a small number of participants. In most
cases, studies move into Phase III testing only after an agent
shows promise in Phases I and II. Phase III trials may include
hundreds of research centers around the country and hundreds
or thousands of people.
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National Cancer Institute
April 1999
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