Clinical trials are research studies that involve people. Each study tries to answer scientific questions and to find better ways to prevent, diagnose or treat cancer. See What Is a Clinical Trial? ²

In cancer research a clinical trial is designed to show how a particular anticancer strategy -- for instance, a promising drug, a gene therapy treatment, a new diagnostic test, or a possible way to prevent cancer -- affects the people who receive it. See If You Want To Find Ways To Prevent Cancer...Learn About Prevention Clinical Trials ³.

A clinical trial is one of the stages of a long and careful cancer research process. Getting promising results from testing a new drug on mice, for example, is a preliminary step to human research studies. Treatments that work well in mice do not always work well in people. See How Is a Clinical Trial Planned and Carried Out? ⁴

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 examine whether taking certain medicines, vitamins or food supplements (or a combination) can prevent cancer.

In the agent prevention 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 can people learn about the possible pros and cons of participating in a prevention trial? Through a process called informed consent you will learn what agent(s) the study will test and how, and possible benefits and risks, before deciding whether or not to participate.

Who's eligible to participate in a prevention clinical trial? Each study has its own guidelines for who can participate. Generally, participants are alike in key ways - such as age, gender, whether or not participants are at increased risk of a certain type of cancer, and other factors.

What do prevention trials test? Many prevention trials are designed to compare a promising new agent with a standard one or to no agent. In these studies patients are randomly assigned to one group or another.

Do some people receive a placebo in prevention clinical trials? People assigned to a group receiving "no agent" take a look-alike pill that contains no active ingredient, called a placebo. Remember that participants in prevention clinical trials do not have cancer. In treatment clinical trials -- designed to compare a new treatment for a certain type of cancer with a standard treatment -- placebos are very rarely used.

Where do clinical trials take place? They are underway all over the country - in cancer centers, other major medical centers, community hospitals and clinics, physicians' offices and veterans' and military hospitals in numerous cities and towns around the United States.

Who pays for the participant costs on prevention clinical trials? The coverage of costs varies, and so it is important to ask a doctor, nurse or a staff member from the study to help you determine in advance what costs must be covered by you or your health plan. See Clinical Trials and Insurance Coverage: A Resource Guide ⁵.