What types of clinical trial are there?

For a treatment to enter everyday use, it must pass through different types of clinical trial.

Trials are done in this way so that they:

  • produce results we can rely on
  • are of value to future patients
  • protect you.

Before clinical trials

Extensive laboratory tests will have been carried out before any new anti-cancer treatment is introduced into a clinical trial.

These will have proved that the drug can affect cancer cells and have helped to find out the possible side effects.

The next step is to discover what is the most effective dose that can be given safely to patients. This is called a Phase I study.

Phase I studies

A Phase I study is designed to find out:

  • what is the most effective dose of the drug and how much can be given safely. For example, the maximum acceptable dose and how often the drug can be given
  • whether enough of the drug is circulating in the blood to affect cancer cells
  • the possible side effects of the drug.

There are two problems with this type of study. Firstly, patients treated at the lowest dose may not benefit significantly from the new drug. Secondly, patients treated later at, or near, the maximum dose may have more side effects. Doctors try to raise the dose as quickly and safely as possible while avoiding any unnecessary side effects.

If it is thought that the new drug may be active against particular cancers, patients with those cancers will be selected for the trial. However, finding out which cancers respond best to the drug is the main aim of a Phase II study.

Phase II studies

Doctors use the information gathered in a Phase I study to help decide:

  • the dose of treatment
  • the frequency of treatment
  • the particular cancers which may respond best to the treatment.

Several Phase II trials will be carried out on different cancers so that doctors can find out how active a particular drug is. Only about 20 to 30 patients with each cancer are needed to take part in this early work for each tumour type. They will be watched very carefully for the effects and side effects of treatment using regular check-ups, blood tests, x-rays or scans. If the drug doesn’t work, no more trials will be carried out. However, if a significant number of responses are seen, the doctors will design a Phase III study.

Phase III studies

A Phase III study will try to compare a new treatment with the best treatment currently available and the following are monitored:

  • the effect of the treatment on the cancer
  • how long the effects last
  • the side effects of the treatment
  • any possible longer-term problems which could develop.

If the differences between the new treatment and the existing treatment are small, hundreds of patients may need to take part before one is identified as better than the other. Studies may take place in several different hospitals at the same time, including hospitals in other countries.

Phase III trials are usually randomised and may include a double-blind procedure. Find out more about organising clinical trials.