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What is a Clinical Trial?

Clinical trials are research studies that usually test a new approach to therapy. There are several different ways that trials are designed, but most fall into one of three categories: Phase I, II, or III. Phase III clinical trials focus on a particular disease and ask specific scientific questions which have the long-term goal of defining the best approach to therapy by comparing one therapy to another.

Phase I trials define the initial safety and toxicity of a new drug. In phase I studies the drug is given at a dose expected to be safe based on adult human and/or animal studies to the initial patients and then subsequent patients are given increasing doses of the drug. The dose is increased carefully, usually in 3 patients before going to the next higher dose. In this manner the maximal dose that can be tolerated by patients is defined and can then be used in a larger number of patients to study the anti-tumor activity of the drug in a phase II study.

Phase II trials test the anti-tumor activity of new approaches in which a safe dose has been established in a phase I study. In a phase II trial, a new drug is often used at the maximal tolerated dose that was defined in a phase I study. A number of patients with leukemia are treated with the new drug to determine what portion will respond and for how long and to further define side effects (toxicity). A phase I study can be expanded at the dose level found to be the maximally tolerated dose (MTD) into a test of response, and so a phase I/II study (combined) is also possible.

Phase III trials are large studies that definitively and scientifically test a new treatment in comparison to the current standard treatment to determine if the new approach improves outcome. After agreeing to participate, patients are assigned to new or standard therapy by chance (randomized assignment). Patients who cannot participate in a phase III clinical trial should receive therapy that has been proven in previous clinical trials to be safe and to provide the best chance of achieving long-term survival.

To find out more about Clinical Trials you can visit the NCI's Clinical Trial Information Page.