Clinical trial design

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 very important. Without a control group it is impossible to 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 situations where there is no standard treatment to compare with the trial treatment, patients may be given a placebo. The placebo looks like the real drug but is inactive.

Placebos are also used where a 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.

Some randomised trials are double-blind, 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 particular drug it contains. In an emergency your doctor can always find out from the trial coordinators which treatment you are having, or the pharmacy department at the hospital will be able to break the code.

A blind or double-blind trial aims to reduce any bias. Knowing you were having a new treatment, for example, might make you feel more positive, or more negative, and influence what you report to the researchers. Similarly, if the researchers knew that you were having a new treatment for which they had high hopes, this might affect how they judged your response to it.

All phase 3 and some phase 2 studies are randomised. This means that a computer randomly puts patients into the treatment groups in the trial. Each group has a similar mix of patients of different ages, sex and state of health.

If it were left to the researchers to decide who should get which treatment, they might be influenced by what they know about their patients. Consciously or unconsciously they might put patients 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.

The benefit of randomisation is shown in the diagrams below:

If doctors or patients choose the treatment, it‘s possible that people who are likely to do well will be put in one group, leaving the others for the other group, so the two groups will be different. In that situation, if one group does better than the other, it won’t be clear whether the difference is due to the treatment or because the groups were different.

If the patients are allocated to the treatment groups by a computer, the members of each group can be matched so that both groups are similar. If one group does better than the other group, it is likely to be because of the treatment, as the two groups are the same.