Types and phases of clinical trials

Different types of clinical trials include:

Treatment trials test new treatments or ways to make existing ones better. Maybe it’s new drugs or methods of surgery and radiation. This is the most common type of clinical trial involving people with cancer.

Prevention trials look at new ways to lower the risk of getting cancer or stop it from coming back.

Screening trials look for ways to find cancer early in populations of people, before they have any symptoms.

Diagnostic trials look for better ways to diagnose or stage cancer.

Supportive care trials study how to improve comfort and quality of life for people with cancer or cancer survivors.

Phases of clinical trials

Clinical trials for new treatments are always tested through several steps called phases. Each phase answers specific questions. The most common phases for clinical trials for cancer are:

Phase 1 trials are often the first time a new therapy is tested in people. This phase is used to see how safe a treatment is and what the best dose is. These trials are usually offered to people who have advanced cancer that is no longer responding to treatment or who have no other treatment options. There are usually 15 to 30 people in the trial.

Phase 2 trials are used to show how well a treatment works for a certain type of cancer. They continue to look at how safe the treatment is and what are the possible side effects. There are usually fewer than 100 people in the trial.

Phase 3 trials compare a promising new treatment to the standard treatment, which is the accepted and commonly used treatment for a condition or a disease. In particular, researchers want to know if the new treatment is better than the standard one. Phase 3 trials may include people from all over the world. The usual number of people in the trial is several hundred to several thousand.

Phase 4 trials gather more information on possible effects – good and bad – after a new treatment has been approved for use in Canada. There are usually several hundred to several thousand people in this phase.

Randomized clinical trials

Clinical trials may have different groups in their design. There are 2 groups most of the time, but there can be more. One group is a control group – the people in this group do not get the treatment being studied. The other group is the experimental group – the people in this group get the treatment being studied.

To make sure that the groups can be compared with each other, a computer will assign each person by chance to a group. You have an equal chance that you will be assigned to the control group or the experimental group. This is called randomization.

There are 2 types of randomization.

In blinded randomization, the researchers know who is in the experimental group and who is in the control group, but the people in the study don’t know. This prevents the people in the study from doing things that may affect the study results.

In double-blinded randomization, the people in the trial don’t know what group they are in, and neither do the researchers. In science terms, this study design is thought to be the best because neither the participants nor the researchers can affect the study results by doing things that they think they should, based on what group they are in.

Clinical trials using a placebo

A placebo is a pill or injection that looks like the substance being tested but doesn’t actually do anything. Giving placebos to one group in a clinical trial lets researchers compare the new treatment to the placebo. Placebos are not given instead of effective standard treatments. For example, a trial may compare a new treatment that is given along with the standard treatment to a placebo given along with the standard treatment. This tells researchers whether the new treatment is effective.

Placebos are given in trials that are double-blinded. You will be told if a trial does use a placebo, but you won’t know if you’re in the group receiving it and neither will the researchers.

Expert review and references

  • American Cancer Society. The basics of clinical trials. 2016.
  • American Cancer Society. What are the phases of clinical trials?. 2016.
  • Delacruz A & McCall S . Principles of cancer clinical trials. Yarbro CH, Wujcki D, Holmes Gobel B, (eds.). Cancer Nursing: Principles and Practice. 8th ed. Burlington, MA: Jones and Bartlett Learning; 2018: 9: 227-242.
  • National Cancer Institute. What are clinical trials?. 2016: https://www.cancer.gov/about-cancer/treatment/clinical-trials/what-are-trials.
  • National Cancer Institute. Phases of clinical trials. 2016.
  • National Cancer Institute. Randomization and bias in cancer clinical trials. 2016.
  • Simon RM . Design and analysis of clinical trials. DeVita VT Jr, Lawrence TS, Rosenberg SA. Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2015: 36:398-415.

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