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Clinical trials, also called clinical studies, evaluate investigational methods of treating, diagnosing, and preventing cancer. These investigational methods include approaches to surgery or radiation therapy as well as gene therapy, vaccine therapy, experimental drugs, or various combinations of these treatments.

Clinical trials are among the final stages of a long and careful process of cancer research. Only those treatments that show promising results in tests done in the laboratory are used in clinical trials involving people.

There is no guarantee that the investigational approach will produce good results, but if it is effective, trial participants may be among the first to benefit. You will receive detailed information about the trial and should join a trial only after you understand both the possible risks and benefits. Everyone who joins a clinical trial at the National Cancer Institute is cared for by a team of appropriate experts.

Clinical Trial Phases

Clinical trials are usually conducted in a series of steps, called phases:

  • Phase 0 trials use investigational agents that have shown promise in lab studies and for the first time are given to a small group of patients (10 to 15). Small doses of the new agent are given over a short period to confirm that it works safely in humans in the way predicted by earlier lab studies. If the agent was designed to reach a specific target in cancer cells, tests will be done to check on its success. Any side effects are carefully monitored.

  • Phase I trials test investigational treatments in a small group of patients. In these studies, researchers evaluate what dose is safe, how a new agent should be given (by mouth, injected into a vein, or injected into the muscle), and how often. Researchers watch closely for any harmful side effects. Phase I trials usually enroll a small number of patients and take place at only a few locations. The dose of the new therapy or technique is increased a little at a time. The highest dose with an acceptable level of side effects is determined to be appropriate for further testing.

  • Phase II trials study the safety and effectiveness of an agent or intervention, and evaluate how it affects the human body. Phase II studies usually focus on a particular type of cancer, and include fewer than 100 patients.

  • Phase III trials compare a new agent or intervention (or new use of a standard one) with the current standard therapy. Participants are randomly assigned to the standard group or the new group, usually by computer. This method, called randomization, helps to avoid bias and ensures that human choices or other factors do not affect the study's results. In most cases, studies move into phase III testing only after they have shown promise in phases I and II. Phase III trials often include large numbers of people across the country.

  • 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.
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