Phases of Clinical Trials

Approved by the Cancer.Net Editorial Board, 09/2017

A full-text transcript is available.

Before starting a clinical trial, doctors must prove there is a chance that the new treatment or procedure will work better than what is currently available. They do research until they can prove this. Doctors do clinical trials to test many things, including:

  • A new treatment or medical procedure

  • A new combination of existing treatments

  • A new surgery

  • New medical equipment

  • Changes in daily life, such as eating habits, exercise, or counseling

They might test the treatment on laboratory animals before testing it in people. This is to make sure it is safe to test in people.

The phases of clinical trials

Each clinical trial follows certain steps, called phases. The steps are designed to keep people safe in the clinical trial. Sometimes, steps (phases) are done together, at the same time. Making sure all the steps are done helps protect patients and give accurate results about what the clinical trial is testing.

You can join any phase of a clinical trial if it is an appropriate option for you and the type and stage of cancer that you have. View a chart about the different phases of clinical trials (PDF).

Phase I clinical trials

Doctors do phase I clinical trials to learn if a new drug, treatment, or combination of treatments is safe for people.

In a phase I clinical trial, doctors collect information on:

  • The dose or treatment

  • When and how often people take it

  • Any side effects or problems

  • How your body responds to the treatment. For example, how it affects the cancer or cancer side effects.

If you join a phase I clinical trial, you could be one of the first people to get a promising new drug or treatment.

Phase I clinical trials last several months to a year. They usually have 10 to 30 volunteers. The treatment might help the cancer, and the clinical trial information can help other patients in the future.

Phase II clinical trials

Phase II clinical trials tell doctors more about how safe the treatment is and how well it works. In phase II clinical trials, doctors also test whether a new treatment works for a specific cancer. They may measure the tumor or take blood samples to learn if the treatment is working. Or they might ask you to keep a log of your daily activities and symptoms. They may also check how well you can do certain activities.

A Phase II clinical trial lasts about 2 years. Sometimes, volunteers in phase II clinical trials take different treatments. For example, a phase II clinical trial could have 2 groups:

  • Group 1 – People taking the regular treatment (also called the standard treatment)

  • Group 2 – People taking the regular treatment, plus a new treatment that doctors are studying in the clinical trial

In another example, a phase II clinical trial could have 3 groups. Volunteers in each group get a different dose of the new treatment doctors are studying.

If a phase II clinical trial shows the treatment is likely to work and is as safe as a regular treatment, doctors can do a phase III clinical trial.

Phase III clinical trials

Phase III clinical trials test a new treatment that has worked well for patients in a phase II clinical trial. Doctors compare the clinical trial treatment with the standard treatment. Standard treatment means the best treatment known. The research team needs to learn if the new treatment is better than the standard treatment, has fewer side effects, or both. This means that they need to assign people to different groups as part of the clinical trial. The people in each group get a specific type of treatment, and the treatments are different between groups.             

What is “randomization”?

“Randomization” means assigning people in a clinical trial into different groups. Doctors use a computer program to do this. Using a computer keeps the research team’s opinions from affecting who gets which treatment. This is very important when doctors are comparing 2 or more treatments.

Phase III clinical trials can take many years. They usually have up to several thousand volunteers. The volunteers need to include men, women, and people of all ages and racial and ethnic groups. This helps doctors learn how the treatment works in many different people.

If a phase III clinical trial shows that the treatment works well for a specific cancer, doctors might begin using it with people outside of the clinical trial. For example, if they learn that a certain amount of exercise helps make cancer less likely, they publish a report to share the information with other doctors. If they learn a new medicine is safe and effective, they can ask the government to approve it for people to use. In the United States, that is the Food and Drug Administration (FDA). The FDA looks at the clinical trial results. If this information meets their standards, the treatment is approved.

How is a clinical trial “phase” different from a cancer “stage”?

The stages of cancer are different from clinical trial phases, even though both use the same numbers of 0, 1, 2, 3, and 4. A clinical trial phase does not match your cancer stage. You can have any stage of cancer and be in any phase of clinical trial. This is because the numbers describe different things. The “phase” of a clinical trial is a way to describe the purpose of the clinical trial and how many people are in it. The “stage” of a person’s cancer describes:

  • How much the cancer has grown and spread

  • What type of cancer cells are present. Some types of cells mean the cancer is more aggressive, or likely to get worse, and some do not.

Do I need to be in all the phases of a clinical trial?

No. You can join any phase of a clinical trial if it is open to you. For example, you may join a phase II clinical trial of a specific treatment even if you didn’t participate in the phase I clinical trial of that treatment.

Learn more with free videos

PRE-ACT, Preparatory Education About Clinical TrialsYou can watch a free series of educational videos on Cancer.Net. The series is called Preparatory Education About Clinical Trials, or PRE-ACT.

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Related Resources

More Information

Clinicaltrials.gov