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Clinical trials explained

Cancer clinical trials are research studies that use volunteers to test new ways (interventions) to diagnose, treat and manage cancer. If a trial proves that a test, treatment or other intervention is better than existing options, it may become the new standard of care for patients in the future.

A medicine or another intervention can be developed in a laboratory and tested on animals, but it is only once it has been tested on the human body that we can know it works in people. It also has to be tested on enough people to show that any benefit is not just a random effect for a single person.

A clinical trial will be designed to answer a particular type of research question.

Treatment trials – These test new treatments, new ways of giving  existing treatments, or new combinations of treatments. They look at whether the treatment works and if it causes side effects. The treatments that can be tested include: medicines (chemotherapy, immunotherapy, targeted therapy and other drugs); medical devices; radiation therapy; surgical techniques; nutrition advice; physiotherapy; exercise programs; psychological therapies; and complementary therapies.

Most cancer clinical trials in Australia are treatment trials. The information on these pages mostly relates to treatment trials.

Prevention trials – These work out whether medicines and health programs lower the risk of developing diseases such as cancer.

Screening trials – These look at new methods of detecting diseases before symptoms appear.

Diagnostic trials – These identify more accurate or easier tests for diagnosing a particular disease in people who have signs or symptoms.

Quality of life trials – These test ways to improve the comfort and quality of life of people who have cancer. They are done alongside a treatment trial.

Registry trials – For most treatment trials, you will have the treatment as part of the trial. Another way researchers can compare how well different treatments work is through registry trials. A registry trial collects information from people with a particular type of cancer who are having routine treatment. It can’t be used for testing new treatments, but it can answer a range of questions about existing treatments.

Your cancer treatment team may talk to you about joining a registry trial. If you choose to join the registry, you agree to share your health information, such as your medical history, the treatments you are having and the results of tests. This information will then be compared with information from many other patients to work out which treatment approaches are the most effective.

Registry trials are a cost-effective way to run a clinical trial and they allow many more people to participate in cancer research.

Researchers spend many years developing new treatments or medicines in the laboratory before involving people. They then plan the clinical trial to progress in a series of steps called phases. Every phase considers whether the risks outweigh the benefits. Information gathered in each phase determines whether the study can move on to the next phase, and whether the drug or treatment is approved for use. There can be up to four phases, but not all clinical trials go through every phase.

How clinical trial phases work

Phase 1 – Safety

How many people take part (participants) = 10-100

What it aims to do (purpose)

  • first study in people
  • tests safety of new treatment
  • finds the safest dose and the best way it can be given, identifies side effects and checks how the treatment works with other medicines or food (interactions)
  • often includes people with different types of cancer

How it works

  • participants are given a fixed dose and watched closely for side effects
  • the dose is often small in the first group of participants, and then gradually increased in the next groups until any side effects outweigh the potential benefits

More information

  • may involve overnight stay in hospital for monitoring
  • people may benefit but often don’t see big improvements

Phase 2 – Effectiveness

How many people take part (participants) = 100-300

What it aims to do (purpose)

  • builds on the results of the phase 1 trial
  • continues to test safety of the new treatment
  • begins to assess how well the new treatment works on the disease

How it works

  • often focuses on one type of cancer
  • the participants may be put into separate groups and given different treatments (randomised controlled trial) or they may all have the same experimental treatment (non-randomised trial)

More information

  • people often have treatment as an outpatient

Phase 3 – Comparison

How many people take part (participants) =100s-1000s

What it aims to do (purpose)

  • tests if the new treatment is better than the best currently available treatment (standard treatment)
  • compares side effects, survival and quality of life
  • collects information that allows new treatments and existing treatments to be used in new ways or for different diseases

How it works

  • uses two or more treatment groups – experimental and control
  • usually groups are randomised and sometimes blinded
  • a placebo may be used for comparison
  • runs over a longer period of time

More information

  • some phase 3 trials help the Therapeutic Goods Administration (TGA) work out whether to approve a new drug for use in Australia

Phase 4 – Follow-up

How many people take part (participants) = 1000s

What it aims to do (purpose)

  • identifies how well the new treatment works when used more widely in the real world
  • monitors the long-term benefits and risks
  • looks for other uses of the treatment
  • sometimes known as an expanded access study

How it works

  • carried out after the treatment has been approved by the TGA
  • usually run by pharmaceutical companies that make the product
  • some people are able to get early access to new drugs before the cost is covered by the Pharmaceutical Benefit Scheme (PBS)

More information

  • not all treatments go through a phase 4 clinical trial
  • phase 4 trials are less common than phase 1–3 trials

It is important for researchers to know that the results of a study are accurate and not caused by chance. This means they must follow strict guidelines. Researchers also need to make sure their own – or the participants’ – ideas or beliefs about the research don’t unfairly influence the results. There are various ways to make sure clinical trials are fair and reliable.

Many clinical trials are randomised controlled trials (RCTs). A randomised controlled trial helps prevent bias, so it is the best way to test if a new treatment works. (Bias occurs when the results of a trial are affected by human choice, expectations or other factors not related to the treatment being tested.)

Most phase 3 trials and some phase 2 trials are randomised. This means participants in the study are put into two or more groups (known as treatment arms) at random. The two groups then receive different treatments, and the results of the different groups are compared. Researchers cannot choose who goes into each group.

Test or experimental arm – This group is given the new treatment that is being tested. Sometimes, the experimental treatment is given in addition to the current standard treatment.

Control arm – This group receives the current standard treatment for the disease or an inactive treatment known as a placebo.

When randomly allocated groups are compared with each other, it is  possible to work out which treatment is better. This is because researchers can be certain that the results are related to the treatment, and not to any other factors.

How randomisation works

Click on image to enlarge

Standard treatment and placebos

In a randomised controlled trial, people in the control arm may receive the standard treatment or a placebo.

Standard treatment – This is the current most effective treatment given to people for their disease or condition. For example, the standard treatment for early breast cancer is surgery, often followed by chemotherapy, radiation therapy and/or hormone therapy.

In some cases, the current standard of care is for the doctors to monitor the cancer closely with regular tests and check-ups, and only offer treatment if the cancer progresses. This approach may be known as active surveillance or watchful waiting. For example, active surveillance is recommended for some early thyroid cancers that aren’t causing any symptoms and are low risk, since the risks of treatment may outweigh the benefits in this  situation.

Placebo – This is an inactive or “dummy” treatment. It is made to look, taste or feel like the treatment being tested, but it doesn’t have any active (therapeutic) ingredients (if a medicine) or beneficial effect. Examples of placebos are sugar pills and saline injections.

A placebo is used to show whether any improvements are because of the actual treatment or because of other factors linked with being in the study, such as being more closely monitored or simply expecting the treatment to be helpful. If the people on the experimental treatment improve more  than those on the placebo, this provides stronger evidence that it is the experimental treatment that is responsible.

Participants will be told if a study uses a placebo, but they won’t be told which treatment they are having, and the research team usually don’t know either. In cancer treatment trials, placebos may be used:

  • together with the standard treatment – for example, one group gets the existing standard therapy plus the experimental treatment, and the other group gets the standard treatment plus a placebo
  • on their own, but only when there is no existing standard treatment to compare against an experimental treatment.

Blinded studies

In a blinded study, participants don’t know which arm of a study they’re in. Some randomised controlled trials are called double-blind studies as neither the participant nor the research team know who is receiving the experimental or control treatment. In a double-blind trial, the researchers only discover who is in each arm of the study at the end of the trial when the results are being analysed.

Blinding is used only when participants can’t tell the difference between the two types of treatment. It is not used when the control and experimental treatment are noticeably different – for example, it would be hard to hide surgery and massage from the participant.

The aim of blinding is to reduce bias in the reporting of benefits and side effects. If you don’t know which treatment you’re having, the results are less likely to be influenced by your or your doctor’s views. For example, if you or your doctor knew you were having the experimental treatment, you might report that you’re feeling better than you actually are because you believe you are having a more effective treatment. In an emergency, your doctor can find out what treatment you’re having by contacting those running the study.

Crossover studies

In crossover studies, the people in each trial arm receive that treatment for a time and may then have the opportunity to swap to the other  treatment. This can mean all participants have all treatments and helps confirm which is the most effective. If the new treatment doesn’t work as hoped with the first group, the second group won’t cross over. You also won’t cross over if you are doing well on the first treatment.

In a single arm trial, everyone receives the same experimental treatment.  This method may be used for phase 1 and phase 2 trials, or where the  cancer being treated is rare and it is hard to conduct a randomised trial.


Clinical trials are not the only type of clinical research studies. You may also be invited to get involved in behavioural research or translational research.

Behavioural research

Behavioural researchers try to understand why people behave in the way that they do. They study the characteristics, lifestyles and social situations of different people to see how these factors may affect the risk of developing or surviving cancer. They then try to develop ways to prevent or change behaviours that might increase cancer risk or lower survival outcomes. Behavioural researchers also look at the emotional and social impacts of cancer on the person with cancer, as well as the impact on their family and friends.

If you take part in a behavioural research study, you may be asked to fill in surveys or be interviewed about your lifestyle, including your eating, drinking, smoking and exercise habits.

You may also be able to take part in a program aimed at changing these behaviours. For example, you might be offered free counselling, an exercise class or a session on healthy eating. The aim of the programs may be to reduce cancer risk or to improve how you cope with the impacts of cancer.

Psychosocial research

One area of behavioural research is called psychosocial research. This looks at how cancer affects people emotionally, psychologically and socially. In cancer care, this is sometimes called psycho-oncology. Researchers try to understand how patients and carers cope emotionally at different stages of a disease. They develop and test ways to improve people’s ability to deal with the impacts of cancer.

Translational research

Translational research forms a link between laboratory and clinical research, or between clinical research and standard treatments. It aims to get new treatments or medical approaches into practice quickly. It is sometimes called “bench to bedside” research because laboratory research results are directly used to create new therapies and tests. The findings of behavioural and psychosocial research are also translated into information resources for people affected by cancer.

There can also be “bedside to bench” research – for example, hospitals, treatment centres and health professionals may collect information about how well a treatment works to help laboratory researchers work out what to study next.

Featured resource

Understanding Clinical Trials and Research

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This information is reviewed by

This information was last reviewed January 2022 by the following expert content reviewers: A/Prof Brett Hughes, Senior Staff Specialist, Medical Oncology, Royal Brisbane and Women’s Hospital and The Prince Charles Hospital, and Associate Professor, The University of Queensland, QLD; Christie Allan, Clinical Trials Lead, Cancer Council Victoria, VIC; Dawn Bedwell, 13 11 20 Consultant, Cancer Council Queensland, QLD; Joanne Benhamu, Senior Research Nurse, Team Lead, Lung, Colorectal and Palliative Care Trials, Parkville Cancer Clinical Trials Unit, Peter MacCallum Cancer Centre, VIC; Louise Dillon, Consumer; Sabina Jelinek, Clinical Nurse Research, St John of God Murdoch Hospital, WA; Chloe Jennett, Program Coodinator, Cancer Research, Cancer Council NSW; Carmel McCarthy, Consumer; Alison Richards, Research Unit Manager, Medical Oncology Clinical Trials Unit, Flinders Medical Centre, SA; Prof Jane Ussher, Translational Health Research Institute (THRI), School of Medicine, Western Sydney University, NSW; Prof Janette Vardy, Medical Oncologist, Concord Cancer Centre, and Professor of Cancer Medicine, The University of Sydney, NSW.