Skip to Content

What are the Phases of Clinical Trials?

A new treatment goes through several phases. Each phase has a different purpose:

  • Phase I trials test if a new treatment is safe and look for the best way to give the treatment. Doctors also look for signs that cancer responds to the new treatment.
  • Phase II trials test if one type of cancer responds to the new treatment.
  • Phase III trials test if a new treatment is better than a standard treatment.
  • Phase IV trials find more information about long-term benefits and side effects.

Most of the time, when you take part in a clinical trial, you will only be in that one phase of the study. Treatments move through the phases, but patients do not.

Clinical Trial Phases Graph

Phase I Trials

Test if a new treatment is safe in people. Doctors also find the best way to give the treatment. 

The goal of a Phase I trial is to:

  • Find out if a new treatment is safe.
  • Find the best way to give the new treatment, such as by mouth or by vein.
  • See if there are signs that cancer responds to the new treatment.

Phase I trials usually include 15 to 30 patients who are divided into small groups. These groups are called cohorts. The first cohort receives a dose of the new drug. Doctors may collect blood or urine samples to measure drug levels in the patients.

If the first cohort does not have any severe side effects, then a new cohort receives a higher dose of the same drug. The dose increases with each new cohort until the doctors find the best dose for future testing. With each increasing dose, doctors test each patient to see if he or she is responding to the treatment. If the doctors find that the treatment is safe, then it will move forward to be studied in a Phase II trial.

The Clinical Center for Targeted Therapy provides many of MD Anderson’s Phase I clinical trials. Ask your doctor if you would like to learn more about this center.

Phase II Trials

Test if a new treatment works in one type of cancer.

Fewer than 100 patients usually join a Phase II trial. Even though the main goal is to see if the treatment works, doctors still closely watch patients’ side effects. If the new treatment works, doctors may go on to study it in a Phase III trial.

Phase III Trials

Test if a new treatment is better than standard treatment.

Phase III trials may include hundreds to thousands of patients around the country or world. Each patient enrolled in a Phase III clinical trial has a chance of being in one of the following groups:

  • Control group – the group that gets the standard treatment
  • Study group – the group that gets the new treatment being tested

Doctors do not know if the new treatment is better than the standard treatment, but they believe it is as good and may be better.

How are patients put into groups?

A computer decides which patients are in the control group and which patients are in the study group. Patients have a chance of being in either group. The patient and doctor do not decide. It is random and due to chance alone. This helps to avoid bias in the clinical trial. (Bias happens when human choices affect a study’s results.)

Would my doctor know which group I am in?

In single blind studies, patients do not know whether they are in the control or study group, but the doctor does. In double blind studies, neither the patients nor the doctors know which patients are in each group. (In case of an emergency, doctors can find this information in the study file.)

Would I be given a placebo?

A placebo is something that looks like medicine, but is not. If a placebo is used, it is given together with the best standard treatment. This allows doctors to compare standard treatment alone to standard treatment with a new drug. If there isn’t a standard treatment, then the placebo may be given alone, but this is not common in cancer trials.

After the Phase III trial, the FDA reviews the clinical trial results to make sure the treatment is safe and effective for people to use. The FDA decides whether to approve the treatment so that it is available for all patients.

Phase IV Trials

Find more information about long-term side effects.

In Phase IV trials, doctors study treatments that the FDA has already approved. The goal of Phase IV trials is to continue studying side effects of a new treatment. 

Request an Appointment

Clinical Trials Booklet

Contact Us

Appointments available
Questions? Need help?

Call askMDAnderson

1-877-632-6789

Find Clinical Trials

Clinical trials are research studies that test new cancer drugs, diagnostic procedures and therapies on humans.


© 2014 The University of Texas MD Anderson Cancer Center