There are several types of trials including prevention, screening, treatment and quality of life (supportive care).
Prevention
trials look at whether certain substances such as vitamins or drugs, diet changes, or lifestyle changes can lower the risk of cancer.
Screening
trials test methods of finding cancer before a person has any symptoms. This is done by researchers studying lab tests and imaging procedures that may detect specific types of cancer.
Treatment
trials look at new treatments and new combinations of existing treatments.
Quality of life
(supportive care) trials allow scientists to study ways to improve the comfort and quality of life of people with cancer. For example, doctors may study drugs that reduce the side effects of chemotherapy or they may explore ways to prevent weight loss or control pain.