Types of clinical trials

In most trials patients are split into two groups. One group will have the standard treatment for their cancer type. The other group will have the trial treatment which is being tested. The results are then compared to see which treatment works and if the side effects are worse or better.

When there isn’t a standard treatment available, one of the groups is given a placebo treatment instead. This is an inactive treatment which looks like a real one.

To decide who goes into each group in a fair way, a computer places patients into treatment groups. This is called randomisation.

You may not be told which treatment group you are in. In some trials, neither the patient nor the doctor will know which treatment they are receiving.

Clinical trials

If you are asked to take part in a phase 2 or phase 3 trial, you may hear terms such as controlled trials, placebo, randomisation, blind trials and double-blind trials.

Controlled trials

In most trials, one group of patients will have the trial treatment and one group will have the standard treatment. The people having the trial treatment are called the trial group and the people having the standard treatment are the control group. The control group is needed to compare with the treatment group. The results of both groups are compared to:

  • see if there is any benefit from the new treatment
  • see if the side effects are better, worse or different
  • measure how much of the improvement in the patients is due to the new treatment and how much would have happened by chance or is due to standard treatment.

Sometimes standard treatment is to ‘watch and wait’. This means that no treatment is given unless the cancer starts to develop or cause symptoms.


In some situations where there is no standard treatment to compare with the trial treatment, patients may be given a placebo. A placebo is an inactive treatment that’s designed to look exactly like a real one. They can only be used in trials where it’s possible to make the placebo look like the real treatment, for example with some drugs.

Placebos may be used when a therapy, such as a targeted therapy, is being added to the standard treatment to see whether this gives better results. One group of people will be given the standard treatment plus the trial therapy and one group of people will be given the standard treatment plus a placebo.


Most phase 3 and some phase 2 trials are randomised. In a randomised trial, a computer selects patients into the treatment groups. This means that if you agree to take part neither you nor your doctors will be able to choose which treatment you are given.

Trials are often randomised because if the researchers or doctors were to decide who should get which treatment, they might be influenced by what they know about their patients. They might put people who they thought were more or less likely to respond to a new treatment into a particular group. This would introduce bias, making the results unreliable.

Bias can be prevented if people are allocated to the treatment groups by a computer. The computer can match the groups so that they are similar – for example, they can be matched so that each group has a similar mix of patients of different ages, gender or state of health. By using matched groups, if one group does better than another group, it’s likely to be because of the treatment, as the two groups are similar.

Blind trials and double-blind trials

If you take part in a trial of a new drug you may not be told which treatment group you are in. This is called a blind trial. The medicine used will look the same whether it’s the new treatment, standard treatment or a placebo.

Some randomised trials are called double-blind trials, which means that neither you, nor the doctor treating you, know which treatment you are getting. Your doctor opens a specially coded treatment pack and only the trial organisers know which drug it contains. In an emergency, your doctor can find out from the trial coordinators which treatment you’re having, or the pharmacy department at the hospital will be able to break the code.

Blind or double-blind trials aim to reduce any bias. For example, knowing you were having a new treatment might make you feel more positive – or more negative – and influence what you report to the researchers. Similarly, if your doctors or the research nurses treating you knew that you were having a new treatment for which they had high hopes, this might affect how they judged your response to it.

Entry criteria

Clinical trials are often carried out in very specific patient groups. This means that it’s only possible to take part in a trial if you fit the group criteria. For example, the cancer may need to be at a certain stage (the cancer’s size, where it is in the body and whether it has spread). Your cancer specialist can tell you if you’re suitable for a specific trial.

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