What Are Clinical Trials?

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Clinical trials are research studies that involve people. Through clinical trials, doctors find new ways to improve treatments and the quality of life for people with disease.

Researchers design cancer clinical trials to test new ways to:

  • Treat cancer
  • Find and diagnose cancer
  • Prevent cancer
  • Manage symptoms of cancer and side effects from its treatment


Clinical trials are the final step in a long process that begins with research in a lab. Before any new treatment is used with people in clinical trials, researchers work for many years to understand its effects on cancer cells in the lab and in animals. They also try to figure out the side effects it may cause.

Any time you or a loved one needs treatment for cancer, clinical trials are an option to think about. Trials are available for all stages of cancer. It is a myth that they are only for people who have advanced cancer that is not responding to treatment. To look for trials, see Find NCI-Supported Clinical Trials

Every trial has a person in charge, usually a doctor, who is called the principal investigator. The principal investigator prepares a plan for the trial, called a protocol. The protocol explains what will be done during the trial. It also contains information that helps the doctor decide if this treatment is right for you. The protocol includes information about:

  • The reason for doing the trial
  • Who can join the trial (called “eligibility criteria”)
  • How many people are needed for the trial
  • Any drugs or other treatments that will be given, how they will be given, the dose, and how often
  • What medical tests will be done and how often
  • What types of information will be collected about the people taking part

 

Why Are Clinical Trials Important?

Today, people are living longer lives from successful cancer treatments that are the results of past clinical trials. Through clinical trials, doctors determine whether new treatments are safe and effective and work better than current treatments. Clinical trials also help us find new ways to prevent and detect cancer. And they help us improve the quality of life for people during and after treatment. When you take part in a clinical trial, you add to our knowledge about cancer and help improve cancer care for future patients. Clinical trials are the key to making progress against cancer.

Stage What it means
Stage 0
Abnormal cells are present but have not spread to nearby tissue. Also called carcinoma in situ, or CIS. CIS is not cancer, but it may become cancer.
Stage I, Stage II, and Stage II
Cancer is present. The higher the number, the larger the cancer tumor and the more it has spread into nearby tissues.
Stage IV
The cancer has spread to distant parts of the body.

Another staging system that is used for all types of cancer groups the cancer into one of five main categories. This staging system is more often used by cancer registries than by doctors. But, you may still hear your doctor or nurse describe your cancer in one of the following ways:

  • In situ—Abnormal cells are present but have not spread to nearby tissue.
  • Localized—Cancer is limited to the place where it started, with no sign that it has spread.
  • Regional—Cancer has spread to nearby lymph nodes, tissues, or organs.
  • Distant—Cancer has spread to distant parts of the body.
  • Unknown—There is not enough information to figure out the stage.

To learn more about staging for your type of cancer, see the PDQ® cancer treatment summaries for adult and childhood cancers.