Trials are carried out in all areas of medicine, not just cancer. Some trials are huge studies involving thousands of patients. They may take months or years to complete.

Trials can be used to investigate all sorts of things. For example, researchers may try to find out whether a new treatment improves the survival rate for certain cancer patients. Or a trial may look at whether one treatment causes fewer side-effects than another, without being any less effective.

Trials go through several stages or phases. The earliest phase (Phase I) may involve just a few patients. Then, as the trial progresses, in Phase II and Phase III, the treatments are tested on more and more volunteers. Phase III trials find out whether the new treatment is better than the best standard care that is currently available.

The results of clinical trials are important, because they help doctors to make better decisions about the care of their patients.