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- Side effects are carefully assessed and recorded. Patients are also observed closely for anticancer effects by
- repeated measurement of the cancer sites present at the beginning of the trial. If those sites shrink appreciably,
- the patient is said to have responded to the treatment. Phase I treatments may produce anticancer effects and
- some patients have been helped by them.
- • Phase II These studies determine the effect of a research treatment on various types of cancer. Usually,
- groups of 30 to 40 patients with one type of cancer—breast cancer that has become resistant to standard
- therapy, for example—receive a Phase II treatment. Side effects are assessed and, since more people receive the
- treatment than in Phase I, there is more chance to observe less common side effects. Patients are closely
- observed for anticancer effects and response rates are determined. If at least one-fifth of the patients respond,
- the treatment is judged to be active against the tumor type. A treatment that shows activity against cancer in
- this phase moves to Phase III.
- • Phase III Trials in this phase require large numbers of patients—some trials enroll thousands—who are
- divided into groups. One group, called the "control" group, may receive the standard accepted treatment so the
- new treatment can be directly compared to it. The control group may receive the chemotherapy usually given
- for a certain type of cancer, for example, while another group receives the new treatment to see if it improves
- survival. All patients in Phase III trials are monitored closely for side effects, and treatment is discontinued if
- the side effects are too severe.
