Most clinical research involves the testing of a new drug. The study progresses in an orderly series of steps, called phases. This allows researchers to ask and answer questions in a way that gives reliable results about the drug and protects the patients. Clinical trials are usually classified in three phases:

• Phase I trials are the first step in testing a new approach in humans. 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 and what dose is safe. 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 patients are divided into small groups, called cohorts. Each cohort is treated with an increased dose of the new treatment or technique. 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 (a currently accepted and widely used treatment for a certain type of cancer, based on the results of past research) . Participants are randomly assigned to the standard group or the new group, usually by a 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 may include hundreds of people across the country.