Types of clinical trials
Medical research studies involving people are called clinical trials.
There are two main types of trials or studies:
- interventional
- observational
Interventional trials aim to find out more about a particular intervention, or treatment. A computer puts people taking part into different treatment groups. This is so that the research team can compare the groups.
Observational studies aim to find out what happens to people in different situations. The research team observe the people taking part, but they don’t influence what treatments people have. The people taking part aren’t put into treatment groups.
There are different types of trials within these two groups. This page has information about
Pilot studies and feasibility studies
- Multi-arm multi-stage (MAMS) trials
Pilot studies and feasibility studies
Pilot studies and feasibility studies are small versions of studies which are sometimes done before a large trial takes place.
Feasibility studies are designed to see if it is possible to do the main study. They aim to find out things such as whether patients and doctors are happy to take part, and how long it might take to collect and analyse the information. They don’t answer the main research question about how well a treatment works.
Pilot studies are small versions of the main study. Pilot studies help to test that all the main parts of the study work together. They may also help answer the research question. Sometimes the research team include the information collected during the pilot study in the results of the main study.
Prevention trials
Prevention trials look at whether a particular treatment can help prevent cancer. The people taking part don't have cancer.
These trials can be for the general population or for people who have a higher than normal risk of developing a certain cancer. For example, this could include people with a strong family history of cancer.
Screening trials
Screening tests people for the early signs of cancer before they have any symptoms. As with prevention trials, screening trials can be for the general population. Or they can be for a group of people who have a higher than normal risk of developing a certain cancer.
Researchers may plan screening trials to see if new tests are reliable enough to detect particular types of cancer. Or they may try to find out if there is an overall benefit in picking up the cancer early.
Treatment trials
Treatment trials can look at:
- new drugs or combinations of drugs
- new ways of doing surgery or radiotherapy
- new medical devices
- new ways to use existing treatments
- ways to improve the quality of life for people with cancer
Researchers run treatment trials in stages. These stages are called phases. Early phase trials aim to find out about the safety and side effects of a new treatments. Later phase trials aim to see if a new treatment works better than the current treatment. Or if a new treatment works better than a dummy drug (
)
In some trials, you are randomly assigned to a treatment group. This is called a randomised trial. It is the most reliable way to test how a treatment works. We have more information about randomisation.
Some trials look at multiple treatments or groups of people at the same time to speed up research. These include:
- basket trials
- umbrella trials
- multiple-arm multi-stage trials
Basket trials
Basket trials test the same treatment in different types of cancer or cancer subtypes. The people taking part have different cancer types but they all have the same change in their cancer cells. This may be a particular change in the genes or proteins of the cancer cells. These are called molecular changes or alterations.
Umbrella trials
Umbrella trials test multiple treatments in the same type of cancer. There are several treatment groups based on changes in their cancer cells. So those taking part have the same cancer type but may have different molecular changes. Each group may have a different treatment that aims to target this change.
Basket and umbrella trials may or may not have a . This depends on the design of the trial.
Multi-arm multi-stage (MAMS) trials
A multi arm trial is a trial that has:
- several treatment groups as well as
- the standard treatment group (the control group)
These trials have the same control group all the way through. The other treatment groups can change as the trial goes on. As these trials are more complex there are a number of treatments that people might have.
The research team may decide to stop recruiting people to a particular group. This could be because they have enough people to start looking at the results. Or because early results show the treatment isn’t working as well as they’d hoped.
The researchers may add new treatment groups as new drugs become available to look at. This means they don’t have to design and launch a new trial each time they want to research a new treatment. So it helps get results quicker.
The Stampede trial for prostate cancer is an example of a MAMS trial.
Observational studies
The 3 main types of observations studies are:
- cohort studies
- case control studies
- cross sectional studies
Cohort studies
A cohort is a group of people, so cohort studies look at groups of people. In a cohort study, researchers follow a group of people over a period of time to see what happens to them.
For example, a research team might recruit people who do not have cancer and collect information about them for a number of years. The researchers see who in the group develops cancer and who doesn’t. They then look to see whether the people who developed cancer had anything in common, such as a similar lifestyle or exposure to a certain risk factor.
Cohort studies are very useful ways of finding out more about risk factors. But they are expensive and time consuming. They can be used when it wouldn’t be possible to test a theory any other way.
Case control studies
Case control studies work the opposite way to cohort studies. The research team recruit people into two groups:
- a group of people who have a disease (cases)
- a group of people who don't (controls)
They then look back to see how many people in each group were exposed to a certain risk factor.
Researchers want to make the results as reliable as possible. So they try to make sure the people in each group have the same general factors such as age or gender.
Case control studies are useful and they are quicker and cheaper than cohort studies. But the results may be less reliable. The research team often rely on people thinking back and remembering whether they were exposed to a certain risk factor or not. But people may not remember accurately, and this can affect the results.
Another issue is the difference between association and cause. Just because there is an association between a factor and a disease, it doesn’t mean that the factor causes the disease.
For example, a case control study may show that people with a lower income are more likely to develop cancer. But it doesn’t mean that the level of income itself causes cancer. Other factors, such as access to healthcare or healthy food, might play a role in increasing the risk.
Cross sectional studies
Cross sectional studies are carried out at one point in time, or over a short period of time. They find out who has been exposed to a risk factor and who has developed cancer, and see if there is a link.
Cross sectional studies are quicker and cheaper to do. But the results can be less useful. Sometimes researchers do a cross sectional study first to find a possible link. Then they go on to do a case control or cohort study to look at the issue in more detail.
References
Oxford Handbook of Clinical and Healthcare Research (1st edition)
R Sumantra, S Fitzpatrick, R Golubic and others
Oxford University Press, 2016
Systematic review of basket trials, umbrella trials, and platform trials: a landscape analysis of master protocols
JJH Park and others
Trials, 2019.20:572
An overview of precision oncology basket and umbrella trials for clinicians
JJH Park and others
CA:A Cancer Journal for Clinicians, 2020. Volume 70, Issue 2. Pages 125-137
Clinical Trials Toolkit
National Institute for Health and Care Research (NIHR)
Accessed December 2024
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