What types of clinical trials are there

Phase 1 trials are the first stage in testing a new treatment in people. They usually involve a small number of people (around 10-30) who may 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
• 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 further treatment options are available for them. Advanced cancer is cancer that has spread from where it started to other parts of the body.

Phase 1 trials usually take place at specialist cancer centres and there may be a waiting list to join the trial.

If the results of a phase 1 trial are encouraging, the treatment 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 results) 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 what dose to use
• more about the side effects and how to manage them.

If the results of the phase 2 trial are positive the treatment may move into a larger phase 3 trial.

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
• any other problems that could develop, to learn more about how to provide the treatment safely.

Most phase 3 trials are randomised controlled trials (RCTs) and usually involve many more people than phase 2 studies. Larger numbers are needed so that even small differences in results can be seen more easily, which means the results of the trial will be more reliable. Some phase 3 trials are blinded trials.

A new treatment usually has to show better results than the standard treatment before it can be introduced as a treatment in the NHS. Sometimes, a treatment needs to be tested in several trials before it is introduced. But if the trial is big enough and the results are good, several trials may not be needed.

Phase 4 trials are usually carried out soon after new drugs have passed all the previous stages and have been licensed for routine use. Phase 4 trials aim to find out as much as possible about how safe the drug is by monitoring very large numbers of people. They also look at how well the drug works, learn more about side effects and what the long-term risks and benefits are for people taking part. Phase 4 trials aren’t needed for every drug.