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Phases of clinical trials

Phases of clinical research

The phases of clinical research are the steps in which scientists do experiments with a health intervention in an attempt to find enough evidence for a process which would be useful as a medical treatment. In the case of pharmaceutical study, the phases start with drug design and drug discovery then proceed on to animal testing. If this is successful, they begin the clinical phase of development by testing for safety in a few human subjects and expand to test in many study participants to determine if the treatment is effective.

Phases of clinical trials

This page is about the different phases of clinical trials. It has information about

What trial phases are Trial phases at a glance Phase 0 trials Phase 1 trials Phase 2 trials Phase 3 trials Phase 4 trials Trials covering more than one phase

What trial phases are

Clinical trials testing new treatments are divided into different stages, called phases. The earliest phase trials may look at whether a drug is safe or the side effects it causes. Later phase trials aim to test whether a new treatment is better than existing treatments.

There are 3 main phases of clinical trials – phases 1 to 3. Phase 1 trials are the earliest phase trials and phase 3 are later phase trials.

Some trials have an earlier stage called phase 0, and there are some phase 4 trials done after a drug has been licensed.

Some trials are randomised. This means the people taking part are put into one of treatment groups at random. Doing this means the results are more reliable.

Phase 0 trials

Phase 1 trials are usually the earliest trials of drugs in people. But your doctor might ask if you would like to join a phase 0 study. These studies aim to find out if a drug behaves in the way researchers expect it to from their laboratory studies.

Phase 0 studies usually only involve a small number of people and they only have a very small dose of a drug. The dose of the drug is too small to treat your cancer, but you are also less likely to have side effects.

Phase 0 trials aim to find out things such as:

  • whether the drug reaches the cancer cells

  • what happens to the drug in the body

  • how cancer cells in the body respond to the drug

You might have extra scans and give extra samples of blood and cancer tissue (biopsies) to help the researchers work out what is happening.

Phase 1 trial

Phase 1 is sometimes written as phase I. They are usually small trials, recruiting only a few patients. The trial may be open to people with any type of advanced cancer, usually those who have already had all other available treatments.

Phase 1 trials aim to find out:

  • how much of the drug is safe to give

  • what the side effects are

  • how the body gets rid the of drug

  • if the treatment helps shrink the cancer

Patients are recruited very slowly onto phase 1 trials. So even though they don't recruit many people, they can take a long time to complete.

They are often dose escalation studies. This means that the first few patients that take part (called a cohort or group) are given a very small dose of the drug. If all goes well, the next group have a slightly higher dose. The dose is gradually increased with each group. The researchers monitor the side effects people have and how they feel, until they find the best dose.

In a phase 1 trial you may have lots of blood tests because the researchers look at how your body copes with and gets rid of the drug. They carefully record any side effects you may have and when you have them.

The main aim of phase 1 trials is to find out about doses and side effects. They need to do this first, before testing the potential new treatment to see if it works. Some people taking part may benefit from the new treatment, but many won't.

Phase 2 trials

Phase 2 is sometimes written as phase II. Not all treatments tested in a phase 1 trial make it to a phase 2 trial.

These trials can be for people who all have the same type of cancer, or for people who have different types of cancer.

Phase 2 trials aim to find out:

  • if the new treatment works well enough to be tested in a larger phase 3 trial

  • which types of cancer the treatment works for

  • more about side effects and how to manage them

  • more about the best dose to use

These treatments have been tested in phase 1 trials, but you may still have side effects that the doctors don't know about. Treatments can affect people in different ways.

Phase 2 trials are usually larger than phase 1. There may be up to 100 or so people taking part. Sometimes in a phase 2 trial, a new treatment is compared with another treatment already in use, or with a dummy drug (placebo).

Some phase 2 trials are randomised. This means the researchers put the people taking part into treatment groups at random. Find out about randomised trials.

Phase 3 trials

Phase 3 is sometimes written as phase III. These trials compare new treatments with the best currently available treatment (the standard treatment).

Phase 3 trials aim to find out:

  • which treatment works better for a particular type of cancer

  • more about the side effects

  • how the treatment affects people’s quality of life

They may compare standard treatment with:

  • a completely new treatment

  • different doses of the same treatment

  • having the same treatment more, or less, often

  • a new way of giving a standard treatment (radiotherapy for example)

Phase 3 trials usually involve many more patients than phase 1 or 2. This is because differences in success rates may be small. So, the trial needs many patients to be able to show the difference.

Sometimes phase 3 trials involve thousands of people in many different hospitals and even different countries. Most phase 3 trials are randomised. This means the people taking part are put into treatment groups at random. See our information about randomised trials.

Phase 4 trials

Phase 4 is sometimes written as phase IV. These trials are done after a drug has been shown to work and has been licenced.

Phase 4 trials aim to find out:

  • more about the side effects and safety of the drug

  • what the long term risks and benefits are

  • how well the drug works when it’s used more widely

We have information about how drugs are licensed.

Trials covering more than one phase

Most trials are just one phase. But some trials cover more than one phase. For example, the same trial can include both phase 1 and phase 2. So you may see trials written as phase 1/2 or phase 2/3.

Randomised trials have at least 2 different treatment groups. The people taking part are put into one of the groups at random. This process is called 'randomisation' and is usually done by a computer. Most phase 3 trials and some phase 2 trials are randomised.

Often there is one group who have the standard treatment they would have if they weren’t in the trial. They are the control group. People in the other group (or groups) have a new treatment or procedure that is being tested. A randomised trial that has a control group is called a randomised controlled trial (RCT).

Sometimes there is no standard treatment available for the control group. This is could be because people have already had all the treatments currently available, for example. In this situation, the people in the control group would have a dummy treatment, called a placebo.

Why trials are randomised

Researchers run randomised trials because they need to be sure that the results are correct, and there is no bias that could distort the results. Of course, researchers are unlikely to be deliberately biased. But it is possible to be biased without realising it.

For example, doctors may avoid putting patients who are more unwell into a particular trial group without really meaning to. The people in this group then may not do as well as people in another group because they were more unwell to being with. The results would look as if the one treatment works better than the other, but really it doesn't.

The research team put information about the people taking part into the computer program. This might include age, gender and the stage of their cancer. This makes sure that the groups are as similar as possible. That way the researchers know that if one group does better than the other, it’s because of the different treatment and not because of general differences in the people taking part.

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