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Glossary

Clinical Trial Phases

Once a new treatment has been tested in the laboratory and is proven safe for humans, clinical trials begin. Each trial phase is designed to answer specific questions about the treatment.


Phase I

Phase I trials establish the safest dosage and best way to take the drug, and they measure any side effects, or toxicities, of the treatment. They involve a small number of volunteers, usually less than 10014. Since Phase I trials often destroy normal cells as well as cancer cells, studies usually involve patients who have not benefited from standard therapies15.


Phase II

Phase II trials look at the effectiveness of the treatment against cancer and continue to examine safety and side effects. Often, fewer than 100 patients participate and typically they are patients who have tumors or cancer lesions that can be measured before and after treatment16. According to the National Cancer Institute, only one-third of the drugs assessed in Phase II trials are found safe and effective enough to go on to the next phase17.


Phase III

Phase III trials test the effectiveness of a new drug, combination of drugs, or procedure. Unlike the first two phases, Phase III trials require a large number of participants. In cancer studies, patients are not given a placebo, or inactive drug. In studies for cancer drugs, the patients are randomly assigned to receive either the current “gold” standard treatment, which is the best treatment available, or the new treatment. The two treatments are compared for effectiveness. As part of informed consent, patients will receive continual updates on the progress of the trial. If the experimental treatment is not working, patients may choose to leave the trial and take the standard treatment.


Phase IV

Phase IV trials test a drug that is already marketed and available for possible new uses. Phase IV studies also test new dosages and ways of giving the drug.