Clinical trials consist 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.

The National Cancer Institute lists the following benefits for participating in a clinical trial.

• Treatment studies offer sophisticated, up-to-date, cancer care. Patients who do not receive the new treatment receive up-to-date standard care.
  
• If a new treatment or prevention approach is successful, study participants receiving that approach are the first to benefit.
  
• Many people take part in a study to help others who also have cancer, and they feel good about making this contribution.
  
• Exploring all the treatment and prevention options may help a person feel more in control and more a part of vitally important decisions affecting his or her life.
  
• Taking part in a study does not end a continuing relationship with the participant’s primary care physician.