Clinical trials are usually conducted in a series of steps or phases.

• Phase I trials are the first step in testing a new approach in humans. In these trials, researchers evaluate what dose is safe, how a new agent should be given (by mouth, injected into a vein or injected into a muscle) and how often. Researchers watch closely for harmful side effects. Phase I trials usually enroll a small number of patients and take place at only a few locations. The Clinical Research Unit participates in Phase I trials.
• Phase II trials study the safety and effectiveness of an agent or intervention and evaluate how it affects the human body. That is, does the approach work the way it is intended? Phase II trials usually focus on a particular type of cancer and include fewer than 100 patients.
• Phase III trials compare a new agent or new use of a standard agent with a current standard therapy. Participants are randomly assigned to the standard group or the new group, usually by a computer. This method helps to avoid bias and ensures that human choices or other factors do not affect the clinical trial’s results. In most cases, trials move into Phase III only after they have shown promise in Phases I and II. Phase III trials may include hundreds 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 clinical trial.