A clinical trial is a research study that is designed to answer a question about cancer treatment. Preclinical or laboratory studies are performed using animals, human tissue (biopsies), or computer simulations to study the potential effect of experimental drugs, radiation delivery systems or treatment schedules.

Phase I trials are the first step in testing a new treatment on humans. In these studies researchers look for the best way to deliver a new treatment (for example, How much drug or radiation should be given and what is the best way to deliver the new treatment?). Researchers also assess any side effects that result from this new treatment. Since this is the first stage in gathering information about the new treatment only a small number of patients, who would not be helped by other known treatments, are entered on a Phase I study.

Phase II trials focus on learning whether the new treatment has an anticancer effect (for example, Does it shrink or destroy a tumor?). Phase II studies usually involve a small number of patients.

Phase III trials compare two or more treatments to determine which treatment is the best for a particular type of cancer (for example, Which treatment has the best survival rate or local control rate? Which treatment has the fewest side effects?). Phase III trials usually compare the standard treatment to one or more treatments that have shown promise in Phase I and II testing. These trials may involve hundreds or thousands of patients from around the country.

Randomized trials are studies testing two or more treatments. Since it is not known which of the treatments is best, patients are randomly assigned, often by a central office (for example, RTOG Headquarters), to receive a specific treatment. Most often a computer program does this assignment, and the patient has an equal chance of receiving any of the proposed treatments. Neither the patient nor the doctor will know ahead of time which treatment will be assigned. Sometimes drug studies, which can use a placebo (an inactive agent), are “double-blinded,” and neither the doctor or the patient know which treatment is assigned until the study is completed. Randomly assigning treatment arms helps the researchers avoid bias or having the study’s results affected by human choices or preferences. All Phase III trials are randomized, and so are some Phase II trials.