Clinical Trials Terms and Definitions

Types of Clinical Trials

Treatment: These trials investigate the effectiveness of new treatments or new ways of using current treatments. This may include new drugs or new combinations of currently used drugs, new surgical or radiation therapy techniques, or vaccines or other treatments that stimulate a person’s immune system to fight cancer. Combinations of different treatment types may also be tested in these trials.

Prevention: These trials investigate ways of lowering the risk of developing certain types of cancer. Most cancer prevention trials involve healthy people who have not had cancer; however, they often only include people who have a higher than average risk of developing a specific type of cancer. Some cancer prevention trials involve people who have had cancer in the past; these trials study interventions that may help prevent the return (recurrence) of the original cancer or reduce the chance of developing a new type of cancer.

Screening:  These trials investigate new ways of finding cancer early. When cancer is found early, it may be easier to treat and there may be a better chance of long-term survival. Cancer screening trials usually involve people who do not have any signs or symptoms of cancer. However, participation in these trials is often limited to people who have a higher than average risk of developing a certain type of cancer because they have a family history of that type of cancer or they have a history of exposure to cancer-causing substances (e.g., cigarette smoke).

Diagnostic: These trials study new tests or procedures that may help identify, or diagnose, cancer more accurately. Diagnostic trials usually involve people who have some signs or symptoms of cancer.

Quality of life or supportive care: These trials focus on the comfort and quality of life of cancer patients and cancer survivors. New ways to decrease the number or severity of side effects of cancer or its treatment are often studied in these trials. How a specific type of cancer or its treatment affects a person’s everyday life may also be studied.

Phases of Clinical Trials

In order to test new cancer treatments, clinical trials are separated into a series of steps, called phases. If a treatment is successful in one phase, it will proceed onto the next phase for further testing. Some trials are designed to combine phases (phase I/II or II/III) in order to answer research questions more quickly.

Phase I clinical trials are the first-time new therapies are given to people and usually include 15-30 patients. At this stage, researchers are trying to understand the drug’s effectiveness, the best dose to administer, and what side effects may occur. All patients involved in Phase I clinical trials receive a form of active treatment for their cancer; none are administered placebos (looks like a medicine but is not one and is sometimes used in medical research for comparison purposes). If doctors find that the therapy under investigation is safe it will be studied in a Phase II clinical trial.

Phase II clinical trials trials study how well a new treatment works on a certain type of cancer using the dose found in a Phase I clinical trial. Usually fewer than 100 patients join a Phase II trial and they are monitored closely for any side effects from the treatment being studied. All patients who participate in Phase II clinical trials receive active treatment; none are administered placebos.

Phase III clinical trials study therapies that have been safe and effective in the first two stages of testing. Phase III clinical trials study whether a new therapy is better than standard treatment. During a Phase III trial it is unknown if the new treatment is better than standard therapy but it is believed to be as good and may be better. Phase III trials can include hundreds to thousands of patients.

Phase IV trials are conducted to further evaluate the long-term safety and effectiveness of a treatment. They usually take place after the treatment has been approved for standard use. Several hundred to several thousand people may take part in a phase IV study. These studies are less common than phase I, II, or III trials.