What Are Clinical Trials?

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A clinical trial is a research study involving human participants and designed to scientifically answer very specific questions about a particular treatment strategy. For cancer, such questions may involve new drugs, drug combinations, or methods of administering them; new approaches to surgery, radiation, or other therapies; or behavior modification on the part of the participant. The focus of a trial may be on prevention, early detection, treatment, quality of life, or modification of cancer-risk behaviors.

When the study concerns a new pharmacologic agent, it is one step in a long process of lab research, testing, and follow-up. Approximately five out of 5,000 compounds initially investigated in preclinical research (laboratory and animal testing) make it to clinical testing on humans. It takes about 15 years, on average, for an experimental drug to progress from preclinical lab research to approval by the U.S. Food and Drug Administration. One out of five drugs studied in clinical trials is approved by the FDA.

Clinical trials are usually categorized into three phases:

• Phase I trials evaluate the safety of new pharmaceutical compounds in the body, as well as methods for safely administering these drugs, including dosage and delivery (such as oral, injection, and intravenous). These trials involve a small number of patients -- usually no fewer than 20 and no more than 80.

• Phase II trials measure a new treatment's efficacy, or how well it works, and may also gather additional information. Phase II trials typically involve 100 to 300 patients.

• Phase III trials compare a new strategy to an approach that is already in use. These studies involve larger numbers of patients -- typically 1,000 to 3,000. Participants are randomly selected to either receive the new treatment or the standard one, and data from the two groups are compared.

Clinical trials are devised around a plan, or protocol, that specifies the parameters of the study, including:

• the treatment to be studied

• eligibility criteria determining who may be able to participate (factors relating to health, treatment safety, age, and disease stage)

• what information will be gathered (such as maximum tolerated dose, safety, and benefits).

Protocols are reviewed for approval by one or more bodies associated with the research institution. The UCSF Helen Diller Family Comprehensive Cancer Center requires approval from three groups:

• The Site Committee evaluates protocols from the standpoint of a particular cancer site, organ, or type of disease, so that available resources can be applied to the most promising new treatments.

• The Protocol Review Committee evaluates the scientific integrity of the protocol, ensuring that the study will yield useful data and that it will answer the questions it has raised.

• The Committee on Human Research considers the ethics and risks that apply to a particular study. In many institutions, this committee is called the Institutional Review Board, or IRB.

Other checks and balances include safety and data monitoring committees for Phase III trials.

More Information

For further discussion of cancer-related clinical research and the clinical trials process, visit these resources:

The National Cancer Institute publishes a guide, What Is a Clinical Trial?, with links to other NCI resources presented clearly in question-and-answer format.

The Coalition of National Cancer Cooperative Groups has produced several educational modules that provide answers to questions such as "What is a cancer clinical trial? Why is it important? Where are cancer clinical trials conducted? Who conducts and pays for them? and How can I get involved?"