Most clinical research that involves testing a potential new treatment progresses in a sequence of steps called phases. These are highly-regulated activities that allow researchers to pose questions that result in reliable information about the drug and protect patients. For the most part, clinical trials are classified into one of three phases:
Phase I Trials
These are the first studies done with people to evaluate how a new drug should be given (by mouth, injected into a vein, or injected into the muscle), how often, and what dose is safe. A phase I trial usually enrolls only a small number of patients, sometimes as few as a dozen. The research treatment has already been well tested in laboratory and animal studies but no one knows how human patients will react. It may involve significant risk for this reason.
Phase II Trials
A phase II trial continues to test the safety of the drug, and begins to evaluate how well the new drug works against a particular kind of cancer.
Phase III Trials
These studies test a new drug, a new combination of drugs, or a new surgical procedure compared to the current standard treatment. A participant will usually be assigned to the standard group or the new group at random. Phase III trials often enroll large numbers of people and may be conducted at many doctors' offices, clinics, and cancer centers nationwide.