Clinical trials are medical research trials involving patients. Patients take part in trials in all areas of medicine, not just in cancer and not just to test treatment. A clinical trial might also be used to compare different ways of diagnosing an illness, or it might test techniques for preventing a particular cancer.
Carrying out clinical trials is the only way to find out if a new approach to cancer care is better than the standard approach currently used. Without trials it would be very difficult to improve the prevention, screening, diagnosis and treatment of cancer. There would also be a risk that patients could be given treatments that could be harmful.
Trials are more commonly used with some cancers than with others. For example, there are often more trials for cancers that affect a lot of people, like breast cancer or bowel cancer, and fewer trials for rarer types of cancer, such as cancer of the pancreas.