Clinical trials that involve the testing of new treatments for breast cancer progress in a series of steps or phases. Usually, clinical trials in breast cancer are classified into one of three phases:
Phase I trials: These first studies of a new treatment for breast cancer patients evaluate how the new treatment should be given. For example, if the new treatment is a drug, the trial attempts to answer how should the drug be given (by mouth, injected into the blood, or injected into the muscle), how often should the drug be given, and what dose of the drug is safe. A phase I trial usually enrolls only a small number of patients, sometimes as few as a dozen patients.
Phase II trials: In a Phase II trial of a new treatment for breast cancer, usually a particular type or stage of breast cancer is studied. The Phase II trial continues to test the safety of the treatment, and begins to evaluate how well the new treatment works.
Phase III trials: In a Phase III trial of a new treatment for breast cancer, usually the effects of the treatment are studied in a large number of patients. Phase III trials test a new type of therapy (such as a new surgical procedure or a new drug) or a new combination of therapies, in comparison to the current standard of treatment. A patient participating in a Phase III trial usually will be assigned at random to either the standard treatment group or the new treatment group.