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What types of clinical trials are there?

Before any new treatment is tested in a clinical trial it is properly tested in a laboratory. If it works well, the next stage of testing is called a Phase 1 study. A treatment must then pass through different types of clinical trials, known as phases.

Phase 1 trials

These are the first stage in testing a new treatment in people. They usually involve only a small number of people, who often have different types of cancer. The aim is to find out:

  • the safe dose of a drug and how often it can be given
  • what the side effects might be and how quickly people recover from them
  • how well the body copes with the drug
  • any early signs that the drug may have an effect on the cancer.

People who join phase I trials usually have advanced (metastatic) cancer and no other treatment options are available for them. Occasionally, new drugs may be tested in combination with standard drugs. These types of tests usually involve people who are in the early stages of their cancer treatment.

The trials usually take place at certain specialist cancer centres and there may be a short waiting list to join the trial.

Phase 2 trials

Some treatments tested in a phase 1 trial will move to a phase 2 trial. A phase 2 trial usually involves more people – there may be as many as 100 people taking part. In the phase 2 trial, the research team will know which dose to use (from the phase 1 trial) and will want to learn more about how effective this may be for specific types of cancer. The aim is to find out:

  • whether the new treatment works well enough to test it in an even bigger trial (a phase 3 trial)
  • more information about the chosen dose to use
  • more about the side effects and how to manage them.

A phase 2 trial usually focuses on one type of cancer, but sometimes different types of cancers may be included, depending on what treatment is being tested.  These types of trials usually take place at specialist cancer centres. If the results of the phase 2 trial are positive the treatment may move into a larger phase 3 trial.

Randomised controlled trials (RCT)

Some phase 2 trials are randomised. This means that there are at least two different groups in the trial and the people taking part are selected at random for one of the groups. One group will have the new treatment and the other group will have the standard treatment, or a placebo, depending on the trial.

A placebo

Sometimes phase 2 trials compare an existing treatment with either a new one or with a placebo. A placebo is a “dummy” drug”. It is used in clinical trials if there is no standard treatment to compare the new treatment with, or if the treatment being tested is being added to the standard treatment.

The people taking part in the trial may not know whether they are receiving the active treatment or the placebo. This is called a blinded trial. The research team will continue to give them the best level of medical care, whichever treatment they are having.

The placebo effect

Even though a placebo doesn’t actually treat the cancer, it can affect how some people feel. For example, they might feel better because they think they are getting a treatment for their cancer (even though they aren’t). A change in a person’s symptoms as a result of getting a placebo is called the “placebo effect”. It’s important to be aware of the placebo effect when testing a new treatment so that it doesn’t affect the results of the trial.

Phase 3 trials

Phase 3 trials compare new treatments with the best treatment currently available. They can do this by directly comparing a new treatment with an existing one, or by comparing different doses or different ways of giving the treatment.

A Phase 3 trial will also look at:

  • how effective the treatment is
  • any side effects and how long they last
  • any other problems which could develop, to learn more about how to deliver the treatment safely.

Most phase 3 trials are randomised controlled trials (RCT) and usually involve more people than phase 2 studies. Larger numbers are needed so that even small differences in results can be seen more easily.

In some phase 3 trials, people taking part aren't told which treatment they are getting – this is called a blind trial.  If neither the person taking part nor the clinical team know which treatment, this is called a double-blind trial. This information is kept confidential until the end of the trial, although it can be accessed if needed.  

A new treatment usually has to show better results than the standard treatment before it can be introduced as a treatment in the healthcare system. It also has to show that it is good value for money. Sometimes, a treatment needs to be tested in several trials before it is introduced. But if a trial is both good and big enough it may not need several trials.

Phase 4 trials

Phase 4 trials are carried out after new drugs have passed all the previous stages and have been licensed for use. They aim to find out as much as possible about how safe the drug is, and involve very large numbers of people. A phase 4 trial will also look at how well the drug works, learn more about side effects and what the long-term risks and benefits are for participants. Phase 4 trials are not needed for every drug.

Published April 2016

Review date April 2018

Information Standard