Clinical trial design
If you’re 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.
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 compared against the treatment group. The results of both groups are compared to:
see if there’s 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, the 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 trial 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. People who take part in a trial that uses a placebo won’t know whether they’re getting the actual treatment or the placebo.
Most phase 3 and some phase 2 trials are randomised. In a randomised trial, a computer places patients into treatment groups. This means that if you agree to take part, neither you nor your doctors will be able to choose which treatment you’re 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. This means they might put people who they think are 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 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.
Blind trials and double-blind trials
Back to top
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. This means that neither you nor the doctor treating you will know which treatment you’re 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 trials or double-blind trials aim to reduce any bias. For example, knowing you’re having a new treatment might make you feel more positive or more negative. This could influence what you report to the researchers. Similarly, if your medical team knew that you were having a new treatment for which they had high hopes, this might affect how they judged your response to it.
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 (staging takes into account the cancer’s size, position in the body and whether it has begun to spread). Your cancer specialist can tell you if you’re suitable for a specific trial.