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How They Work

Through clinical trials, researchers learn which approaches are more effective than others. This is the best way to test potential new treatments. A clinical trial is a kind of research that involves an experimental treatment and people. Clinical trials help researchers answer questions such as:

  • Is a new treatment or medical device safe?
  • Does the new treatment do what it is supposed to do?
  • Is the new treatment better than a current treatment?
  • Which patients benefit the most from the new treatment?

Clinical trials for some conditions involve a placebo, however, placebos are almost never used in cancer treatment clinical trials. You will be told in advance if the study uses a placebo.

Clinical trials are conducted in phases. Researchers try to answer a different question in each phase. Each phase needs a different set of participants. New treatments must prove to be safe and effective in clinical trials before they can be made widely available.

The four phases of clinical trials are:

Phase I: Is it safe?

The main goal of a Phase I study is to see if the treatment is safe. People in Phase I studies may be healthy or ill. A phase I trial usually enrolls only a small number of patients, sometimes as few as a dozen. These first studies in people evaluate how a new drug should be given (by mouth, injected into the blood, or injected into the muscle), how often, and what dose is safe. This is the first time that a new treatment is tested in people.

Phase II: Does it work?

Once a treatment is safe, then a Phase II study is done to see if the treatment works for particular disease/diseases. Phase II studies usually have more participants than Phase I studies. Phase II studies usually focus on a particular type of cancer. The phase II trial continues to test the safety of the drug, and begins to evaluate how well the new drug works compared to existing treatments. Some Phase II studies may use ‘randomization’ as a means of starting to compare effectiveness of treatment options (see next section).

Phase III: Is it better than what we have now?

A Phase III study compares a new treatment with a current treatment to see which is safer and works better. Phase III trials often enroll large numbers of people, sometimes thousands.

Participants in Phase III trials may be assigned to a control group or to an experimental group. This process is called randomization and is used to prevent unintended bias in test results based on human choices or other factors not related to the treatments being tested. If the trial you are considering uses a randomization process, you will see the trial described as a “randomized clinical trial.” That means you have an equal chance of being assigned to the control group or to the experimental group. The doctor does not, and cannot, choose the group for you.

If you are assigned to the control group, you will get the most widely accepted treatment (standard treatment or "standard of care").

If you are assigned to the investigational group, you will get the new treatment being tested.

Comparing the control and investigational groups often clearly shows which treatment is more effective or has fewer side effects.

After a Phase III study shows that a treatment works and is safe, then the Food and Drug Administration (FDA) reviews it for approval. If the drug or treatment is approved, researchers may do a Phase IV study.

Phase IV: What else can happen?

Phase IV studies look at whether the treatment is useful for other conditions or has long-term problems.

For more information about clinical trials in general, see the National Institutes of Health.