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How are trials divided into phases

Clinical trials are carried out in phases, each designed to find out certain information. Patients may be eligible for studies in different phases depending on their general condition and the type and stage of their cancer. More patients take part in the later phases of studies than in the earlier ones.

In a Phase I study, a new research treatment is given to a small number of patients. The researchers must find the best way to give a new treatment and how much of it can be safely given. They watch carefully for any harmful side effects. The research treatment has been well tested in laboratory and animal studies, but no one knows how patients will react. Phase I studies may involve significant risk for this reason. They are offered only to those whose cancer has spread and who would not be helped by other known treatments. Phase I treatments may produce anticancer effects, and some patients have been helped by these treatments.

Phase II studies determine the effect of a research treatment on various types of cancer. Each new phase of a clinical trail depends on and builds on information from an earlier phase. If a treatment has shown activity against cancer in Phase II, it moves to Phase III.

Here it is compared with standard treatment to see which is more effective. Often researchers use standard therapy as the base to design new, hopefully better, treatments. Then in Phase III, the new treatment is directly compared to the old.

In Phase IV studies, the new research treatment becomes part of standard treatment in patient care. For example, a new drug that has been found effective in a clinical trial can be used together with other effective drugs, or with surgery and/or radiation therapy.

The above information is taken from "What Are Clinical Trials All About?" published by the National Institutes of Health, National Cancer Institute