There are three different kinds (known as phases) of trial. Each phase aims to find out something different about the new treatment or procedure.
Phase I trials
These test possible new treatments on people for the first time and is the earliest stage of testing new drugs on humans. Any new drugs will already have been tested in the laboratory or in animals. These trials are carried out in a very small number of patients, usually those with advanced cancer and who have had all available standard treatment.
They help us to find the correct dose and look at any possible side effects.
Phase II trials
These trials test to see whether a treatment is likely to be effective at the dose(s) chosen. They are not always about introducing a new drug but sometimes testing whether an existing therapy can be given in a different way to be more effective. They will again involve a relatively small number of patients.
Phase III trials
If the results from Phase I and Phase II trials suggest a drug or treatment is both safe and effective, it will then be compared with the current or 'standard' treatment in a Phase III trial. These trials involve larger number of patients and usually run for much longer that Phase I and II trials. As the number of children with cancer is relatively small, there is often strong international collaboration with overseas research organisations so children across many countries can take part in a clinical trial.