• Treatment Trials test new treatments (like a new cancer drug, new approaches to surgery or radiation therapy, new combinations of treatments, or new methods such as gene therapy).
  
  
• Prevention Trials test new approaches, such as medicines, vitamins, minerals, or other supplements that doctors believe may lower the risk of a certain type of cancer. These trials look for the best way to prevent cancer in people who have never had cancer or to prevent cancer from coming back or a new cancer occuring in people who have already had cancer.
  
  
• Screening Trials test the best way to find cancer, especially in its early stages.
  
  
• Quality of Life Trials (also called Supportive Care trials) explore ways to improve comfort and quality of life for cancer patients.
  

Most clinical research that involves the testing of a new drug progresses in an orderly series of steps, called phases. This allows researchers to ask and answer questions in a way that results in reliable information about the drug and protects the patients. Clinical trials are usually classified into one of three phases:

• Phase I trials: These first studies in people evaluate how a new drug should be given (by mouth, injected into the blood, 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.
  
  
• 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. Phase II studies usually focus on a particular type of cancer.
  
  
• Phase III trials: These studies test a new drug, a new combination of drugs, or a new surgical procedure in comparison to the current standard for treatment. A participant will usually be assigned to the standard treatment group or the new treatment group at random (called randomization). Phase III trials often enroll large numbers of people and may be conducted at many doctors' offices, clinics, and cancer centers nationwide.