Development of new anticancer agents and treatment strategies occurs in four phases. Each phase is designed to determine specific information about the potential new treatment such as its risks, safety and effectiveness compared to standard therapy. The hope is that the new therapy will be an improvement over the previous standard therapy.

Phase I Trials:
This phase is probably the most important step in the development of a new drug or therapy. These trials usually involve a small number of patients for whom other standard therapies have failed or no known alternative therapy is available. Phase I therapy may produce anti-cancer effects and a small number of patients may benefit. However, the primary goals of this phase are to determine anticancer activity in humans, the maximum tolerated dose of the treatment, the manner in which the drug works in the body, the toxic side effects related to different doses and whether toxic side effects are reversible. Upon completion of phase I trials, the information that has been gathered is used to begin phase II trials.

Phase II Trials:
Once the information is gathered and analyzed from phase I trials, phase II trials are designed to determine the effectiveness of the treatment in a specific patient population at the dose and schedules determined in phase I. These trials usually require a slightly higher number of patients than phase I trials. This number may increase depending on the number of responses as the phase II trial progresses. Drugs or therapies that are shown to be active in phase II trials may become standard treatment or be further evaluated for effectiveness in phase III trials.

Phase III Trials:
Phase III trials compare a new drug or therapy with a standard therapy in a randomized and controlled manner in order to determine proof of effectiveness. Phase III trials require a large number of patients to measure the statistical validity of the results because patient age, sex, race, and other unknown factors could affect the results. To obtain an adequate number of patients, several physicians (investigators) from different institutions typically participate in phase III clinical trials.

Phase IV Trials:
Once the drug or treatment becomes part of standard therapy, the manufacturer of the drug may elect to initiate phase IV trials. This phase includes continued evaluation of the treatment effectiveness and monitoring of side effects as well as implementing studies to evaluate usefulness in different types of cancers.