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Types and Phases of Clinical Trials


Updated January 06, 2013

Understanding the types and phases of clinical trials is important if you are considering taking part in a clinical trial. Clinical trials are divided into both types: The kind of question the study is designed to answer, and phases, or how far along a treatment is in the investigative process.

Types of Clinical Trials:

We often think of clinical trials as a method of studying new drugs, but many different types of trials are in process to evaluate cancer.

  • Prevention trials – Prevention trials look at substances and lifestyle factors that may raise or lower the risk of developing cancer
  • Screening trials – Screening trials study methods to diagnose cancer in its early stages when it is often more curable
  • Diagnostic trials – Diagnostic trials are done to look for the best methods of finding out if a person has cancer, or to accurately determine the stage of cancer that is present.
  • Treatment trials – Treatment trials evaluate the ability of drugs, radiation, surgery, or other measures to treat cancer.
  • Supportive care trials – Supportive care trials are also called quality-of-life trials. They study the ability of a drug or procedure to lessen the symptoms of cancer or symptoms related to the treatment of cancer

Phases of Clinical Trials

Clinical trials are done to determine the safety and effectiveness of a new drug or procedure in people. During this process, the treatment goes through “phases,” beginning with the first use in people through approval for general use by the Federal Drug Administration (FDA).

Phase 1 – Is the Treatment Safe?

After an experimental drug or treatment has been tested in the lab and/or on animals, it enters a phase 1 trial. These trials involve a small number of patients to test safety in humans and determine the correct dose of a drug. These trials also help determine the best way to give the drug, whether oral or intravenously.

Phase 2 – Does the Treatment Work? After determining that a treatment is reasonably safe in people, it enters phase 2 trials. These are done to test for effectiveness – does the treatment work? Since a larger number of people are studied, further information is gained on safety during phase 2 trials.

Phase 3 – Does the New Treatment Work Better than the Standard Treatment?

Phase 3 trials test the new drug or treatment on hundreds or thousands of individuals. These studies are often “double-blind” trials, which mean that neither the patient nor the investigator knows which treatment is being used. They are designed to answer the question of whether or not the new treatment works better, or has fewer side effects, than the standard treatment.

Phase 4 – Is the Treatment Safe over Time?

Phase 4 trials are less common and serve to answer questions after the FDA has already approved a drug for general use. These can address questions such as long-term safety of a drug, or other circumstances in which the drug may be helpful.


National Cancer Institute. Clinical Trials. Updated 04/27/10. http://www.cancer.gov/cancertopics/factsheet/information/clinical-trials

American Cancer Society. Clinical Trials. What you need to know. Accessed 04/03/12. http://www.cancer.org/docroot/ETO/content/ETO_6_3_Clinical_Trials_-_Patient_Participation.asp

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