Understanding Clinical Trials

Charles R. Thomas M.D.The OHSU Knight Cancer Institute takes part in hundreds of clinical trials. Expanding scientific knowledge is a key mission of OHSU, Oregon’s only academic health center. The following information is adapted from the Clinical Trials pages of the National Cancer Institute.

What are clinical trials?

Clinical trials are research studies with human subjects that test ways to prevent, detect, diagnose or treat medical conditions. They play a crucial role in medical breakthroughs by showing which methods safely work.

Clinical trials generally follow years of laboratory research. Scientists test only the most promising medications and methods on people.

Benefits and risks of clinical trials

Possible benefits of participating in a clinical trial:

  • Clinical trials offer early access to new and possibly better treatments.
  • They provide the ability to help advance scientific understanding.
  • They offer the opportunity to contribute to possible advances in patient care.

Possible risks of participating:

  • A treatment might cause side effects or carry unknown risks.
  • A new treatment might be less effective than the standard treatment.
  • The trial may require additional doctor visits and tests.
  • Even an effective treatment might not work for you.
  • Insurance may not cover all costs.

How clinical trials work


A “principal investigator,” usually a doctor, leads the trial. The doctor designs a “protocol” that outlines:

  • The trial’s goal
  • Who can join or “enroll” (the “eligibility criteria”)
  • How many people are needed
  • Any drugs or treatments that will be given, how and how often
  • Any tests that will be done and how often
  • Information that will be collected from participants


Trials often have precise criteria — age, type of cancer, health status and other factors  for participants. It can be important to test medications or treatments on similar people to make sure other factors aren’t playing a role.

Phases of clinical trials

Cancer trials typically span three phases. A trial advances to the next phase only if it’s successful. Learn more from the National Cancer Institute and from the American Cancer Society.

  • Phase 1: These are done to find a safe dose, to find the best way to give a treatment (by mouth or injection, for example) or to see how a treatment affects the body or fights cancer. Phase 1 trials may include 15 to 30 patients.
  • Phase 2: These are done to see if a new treatment has an effect on a particular cancer. They may include fewer than 100 patients.
  • Phase 3: This phase compares the new treatment with the standard treatment (placebos are seldom used in cancer trials). It may involve 100 to thousands of patients.

Patient safety

Informed consent: Before you agree to participate, the research team must thoroughly explain the trial’s purpose, procedures, risks and benefits. They will also explain your rights, including the right to stop at any time. Learn more.

Oversight: Experts review a trial’s protocols before it starts. Members of institutional review boards, or IRBs, evaluate and monitor trials for safety. Trials also may have a data and safety monitoring board, or DSMB. IRBs and DSMBs can stop trials early if needed. The federal Office for Human Research Protections and the U.S. Food and Drug Administration also play important oversight roles. Learn more.

Who pays

Research costs: The trial’s sponsor, such as a drug company testing a new medication, typically pays for the cost of medication, lab tests and imaging done for the trial.

Patient care costs: A patient’s health insurance usually covers costs such as doctor visits, hospital stays, standard treatments and for lab tests and imaging not done for the trial. Learn more.

Questions to ask

Talk with your care team about whether a clinical trial is appropriate for you. You might take a friend or family member along for support and to help ask questions and write down answers. Consider recording the conversation.

Here are questions you might ask. Find more on the National Cancer Institute and American Cancer Society websites.

  • Does this trial make sense for my type of cancer?
  • What are the potential benefits and risks?
  • What are the potential benefits and risks of my other options?
  • What is the purpose of the trial?
  • Why do researchers think the new treatment may be better?
  • How long will I be in the trial?
  • What kinds of tests and treatments are involved?
  • Will they hurt? If so, for how long?
  • What are possible side effects?
  • How could the tests and treatments affect my daily life?
  • How will the doctor know if the treatment is working?
  • Who will be in charge of my care?
  • Who will I contact if I have problems or concerns?
  • What happens if I decide to leave the trial?
  • Will I have to pay for any of the tests or treatments?
  • Will the trial require extra time?

Learn more