Clinical trial results

This page is about the publication of clinical trial results. There is information about

When trial results are available

It can take a long time to get results from a trial. To fully understand the risks and benefits of a new treatment, researchers have to know how well treatments work in the long term.

Sometimes full results, or perhaps partial results (often called an interim analysis) are available in a year or so. But it is more usual for trial results to take between 2 and 5 years and it can take up to 10 years or more.

When research teams analyse trial results, they look at end points. Examples of end points are whether a cancer has shrunk (response to treatment) or how long it is before the cancer starts to grow again (duration of response). How long it take to get full results will depend on what the end point is.

It can take several years to recruit people for a trial. Particularly if it is a large phase 3 trial. Trials often look at differences between treatment groups 5 years after patients have been treated. So, it could be at least 5 years after the last patient finishes treatment before the research team can start to analyse the results.

Factors that affect trial results

Factors that affect how long it takes to get trial results include the following.

Number of people in the trial

A trial that is recruiting 2,000 patients will often take longer to run than one recruiting 100. 

What the trial is looking at

A trial looking at treatment for a rare cancer can often take longer to recruit than a trial for one of the more common cancers, such as breast cancer.

The subject of the trial

Trials looking at the causes of cancer or preventing cancer can take 10 or 20 years to get the full results. This is because the research team need to follow up the people who took part in the trial and see how many of them go on to develop cancer decades later.

Clinical trials results on our website

Since 2009, we have been writing trial results in plain English and putting them on our clinical trials database. On the trials search page, you can tick the results box to show trials that have results available.

We include both early (interim) results as well as results that show long term follow up. We hope to write up the results of all the trials listed on the database since it began in 2000.

Some trial results have already been published in medical journals. Others may not have been published yet but results might have been presented at a conference or made available to us by the researchers running the trial.

Trials without results

Unfortunately, some trials never produce results. If we know that it is unlikely results will ever be available, we say so. This might happen because a trial didn’t recruit enough people to be able to show anything new. Again, we will say if this is the case.

We are not always able to find out why a trial has not reported any results or why the trial team has not made them available to us.

Finding results if you have taken part in a trial

If you have taken part in a clinical trial and want to know the results, the first thing to do is ask your doctor. If the results are available, your doctor should be able to find them for you.

Everyone who takes part in a clinical trial has a patient information sheet (PIS) to read when they join the trial. Once they have read and understood it, they sign a consent form to agree to take part in the trial.

The PIS usually says what will happen to the results of the trial. It is very unusual for the researchers to say that they will let each individual patient know the results. It is much more common to suggest that patients ask their doctor.

Other places to look for trial results

Clinical trial results are usually published in specialist medical journals. There are many different journals published around the world. They contain reports and results of both clinical trials and laboratory research. Some of the most well known medical journals include

You can use a search engine such as Google to look for articles and read summaries (abstracts). But you can't usually see the full articles without a subscription to the journal.

Research papers are not written in plain English and often use many medical, scientific and statistical terms. They can be very difficult to understand if you are not used to reading this sort of information.

Sometimes an organisation or drug company running a trial releases results to the public, especially if the results are very promising. They may send out a press release or put the information on their website.

Systematic reviews

An organisation called The Cochrane Collaboration carries out systematic reviews. These are overviews of all the research into a specific issue.

The reviews look at the published results of all the trials that have investigated a particular treatment in a particular situation. They pull all that information together and draw conclusions.

The reviewers then write a Cochrane Review and this is published in The Cochrane Library. The Cochrane Database of Systematic Reviews is available free in some countries, including the UK.

Reviews like this are very important. It is often not possible to draw firm conclusions from looking at the results of a single trial. But if several have shown the same result, you can be a bit more certain.

How trial reporting can be improved

One criticism of the current trial system is that not all results are necessarily published. There are several reasons for that. The most common is that the treatment being tested wasn’t really any better than the standard treatment.

It is still important to share results though. If all the results are known, it can save money and time by stopping another researcher trying the same thing.

Sharing results of all trials can also help to present balanced information about treatments to doctors. If one trial shows a treatment to be successful and another doesn’t, doctors know that they can’t be too certain about the likely success of that treatment until they know more.

The research community are thinking about the best way to make sure all results are published in the future.

Quality of life studies

Many trials now include a quality of life study. When treatments in a trial work equally well, it is important to find out if there is any difference in how people felt during the treatment.

Even when a trial doesn’t show that one treatment is better than another, the quality of life part of the study may show that one had fewer side effects. An example is that one treatment may be hospital based, while you can take the other at home. Quality of life studies can show up which treatment patients prefer.  

Results from quality of life studies are a very valuable part of results for trials.

Co-ordinating cancer research

Cancer research wasn’t very well organised in the UK in the past. Researchers from different parts of the country then started to work together and share information more and more.

In April 2001 the National Cancer Research Institute (NCRI) was formed to co-ordinate cancer research in the UK.

In 2008 the National Cancer Intelligence Network (NCIN) was launched. NCIN is part of the National Cancer Research Institute and brings together cancer registries, doctors, health service researchers, the Office for National Statistics and others.

The NCRI and the NCIN now share information so that in the future we will have helpful data about

  • How many people get cancer
  • How well treatments work
  • The outcomes of treatment for different types and stages of cancer

Related information

Last reviewed

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

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