Phases of Clinical Trials

Clinical trials to test new cancer treatments involve a series of steps called phases. If a new treatment is successful in one phase, it will proceed to further testing in the next phase. During the early phases (phases 1 and 2), researchers figure out whether a new treatment is safe, its side effects, and its best dose. They also ensure that the therapy has some benefits, such as slowing tumor growth. In the later phase (phase 3), researchers study whether the treatment works better than the current standard therapy. They also compare the safety of the new treatment with that of current treatments. Phase 3 trials include many people to ensure the result is valid.

There are also very early (phase 0) and later (phase 4) clinical trials. These trials are rare. Phase 0 trials are tiny trials that help researchers decide if a new agent should be tested in a phase 1 trial. Phase 4 trials look at long-term safety and effectiveness. They occur after a new treatment has been approved and is on the market.

The following shows the number of patients participating and the purpose of the most common phases. Although the trial phases are explained in the context of drug treatment trials, the same concepts apply to most types of clinical trials.