The following information was adapted from National Cancer Institute (NCI).

Clinical trials are research studies conducted with people who volunteer to take part. Each study answers scientific questions and tries to find better ways to prevent, screen for, diagnose, or treat a disease. People who take part in cancer clinical trials have an opportunity to contribute to the knowledge of, and progress against, cancer.

Clinical trials are sponsored by private organizations and government agencies that are seeking better treatments for cancer or better ways to prevent, screen, or diagnose cancer.

Research with people is conducted according to strict scientific and ethical principles. Every clinical trial has a protocol, or action plan, which acts like a "recipe" for conducting the trial. The plan describes what will be done in the study, how it will be conducted, and why each part of the study is necessary. The same protocol is used by every doctor or research center taking part in the trial.

Participating patients will be closely monitored by a doctor and staff members according to the study plan. The doctor will decide whether it is in the patient's best interest to keep a patient in the study based on the patient's health, side effects of the treatment, and response to the therapy.

Merck-sponsored clinical trials are carefully designed following government regulations and industry standards to safeguard patients.

Each study’s protocol has guidelines for who can or cannot participate in the study. These guidelines, called eligibility criteria, describe characteristics that must be shared by all participants. The criteria differ from study to study. They may include age, gender, medical history, and current health status. Eligibility criteria for treatment studies often require that patients have a particular type and stage of cancer.

Enrolling participants with similar characteristics ensures that the results will be due to what is under study and not other factors. In this way, eligibility criteria help researchers achieve accurate and meaningful results. These criteria also help ensure that people who could be made worse by participating in the study are not exposed to the risk.

Informed consent is a process by which people learn the important facts about a clinical trial to help them decide whether to participate. This information includes details about what is involved, such as the purpose of the study, the tests and other procedures used in the study, and the possible risks and benefits. In addition to talking with the doctor or nurse, people receive a written consent form explaining the study. People who agree to take part in the study are asked to sign the informed consent form. However, signing the form does not mean people must stay in the study. People can leave the study at any time—either before the study starts or at any time during the study or the follow-up period.

The informed consent process continues throughout the study. If important new information is discovered during the study, the researchers will inform the participants. They may be asked to sign new consent forms if they want to stay in the study.

Clinical trials take place in doctors’ offices, cancer centers, other medical centers, community hospitals and clinics, and veterans’ and military hospitals in cities and towns across the United States and in other countries. Clinical trials may include participants at one or two highly specialized centers, or they may involve hundreds of locations at the same time.

Clinical trials are usually conducted in a series of steps, called phases. Treatment clinical trials listed in PDQ®, the NCI’s cancer information database, are always assigned a phase. However, screening, prevention, diagnostic, and supportive care studies do not always have a phase. Genetics clinical trials generally do not have a phase.

• Phase I trials are the first step in testing a new approach in humans. In these studies, researchers evaluate what dose is safe, how a new agent should be given (by mouth, injected into a vein, or injected into the muscle), and how often. Researchers watch closely for any harmful side effects. Phase I trials usually enroll a small number of patients and take place at only a few locations. The patients are divided into smaller groups, called cohorts. Each cohort is treated with an increased dose of the new therapy or technique. The highest dose with an acceptable level of side effects is determined to be appropriate for further testing.
  
• Phase II trials study the safety and effectiveness of an agent or intervention, and evaluate how it affects the human body. Phase II studies usually focus on a particular type of cancer, and include fewer than 100 patients.
  
• Phase III trials compare a new agent or intervention (or new use of a standard one) with the current standard therapy. Participants are randomly assigned to the standard group or the new group, usually by computer. This method, called randomization, helps to avoid bias and ensures that human choices or other factors do not affect the study’s results. In most cases, studies move into phase III testing only after they have shown promise in phases I and II. Phase III trials may include hundreds of people across the country.
  
• Phase IV trials are conducted to further evaluate the long-term safety and effectiveness of a treatment. They usually take place after the treatment has been approved for standard use. Several hundred to several thousand people may take part in a phase IV study. These studies are less common than phase I, II, or III trials.

People who participate in a clinical trial work with a research team. Team members may include doctors, nurses, social workers, dietitians, and other health professionals. The health care team provides care, monitors participants’ health, and offers specific instructions about the study. So that the trial results are as reliable as possible, it is important for participants to follow the research team’s instructions. The instructions may include keeping logs or answering questionnaires. The research team may continue to contact participants after the trial ends.

After a clinical trial is completed, the researchers look carefully at the data collected during the trial before making decisions about the meaning of the findings and further testing. After a phase I or II trial, the researchers decide whether to move on to the next phase, or stop testing the agent or intervention because it was not safe or effective. When a phase III trial is completed, the researchers look at the data and decide whether the results have medical importance.

The results of clinical trials are often published in peer-reviewed, scientific journals. The patient's identity will be protected. Peer review is a process by which experts review the report before it is published to make sure the analysis and conclusions are sound. If the results are particularly important, they may be featured by the media and discussed at scientific meetings and by patient advocacy groups before they are published. Once a new approach has been proven safe and effective in a clinical trial, it may become standard practice. (Standard practice is a currently accepted and widely used approach.)

Adapted from:
National Cancer Institute. Cancer Facts, Clinical Trials: Questions and Answers, dated January 14, 2004. http://cis.nci.nih.gov/fact/2_11.htm . Accessed on October 4, 2005.