What do clinical trial results mean?

This page tells you about the language researchers use when they are talking about trial results. There is information about

Trial end points

There are different ways of measuring how well a treatment works. Researchers call these the trial end points. These sound complicated in scientific language. But they mean simple things such as

  • How many cancers shrink in patients having a particular treatment – this is the response rate
  • How long is it before a cancer comes back or starts to grow again – this is duration of response
  • Does the cancer continue to grow despite the treatment – this is disease progression
  • How long does each group of patients live – this is the survival rate

Response and duration of response

The cancer can completely disappear for a time. This is a complete response. If it shrinks at least by a third, it is a partial response. If your cancer neither shrinks nor grows, it is said to be stable disease.

The cancer coming back again some time after it has disappeared is called relapse or recurrence. When a cancer that has shrunk starts to grow again, it is called progression. The time to relapse or progression is the duration of response.

Disease progression

If a cancer continues to grow while you are having the treatment this is called disease progression. For researchers to classify a cancer as having progressed, the tumour must have increased in size by a fifth (20%) or a new secondary cancer Open a glossary item must have been found.

This type of wording causes confusion sometimes. Generally, we tend to think of 'progress' as a positive thing. But unfortunately, when doctors talk about the 'progress of a cancer' they mean it has grown. For that reason, we generally try to avoid using this particular phrase on our website.


Doctors often follow up patients for 5 or 10 years. Even if the people in the trial recover from their cancer and years later die from something else, this is recorded in the results.

Trial results are often presented as 5 year survival or 10 year survival. This is the percentage of people alive at least 5 or 10 years after their treatment in the trial. It doesn't mean the number of people who live for 5 or 10 years and then die.

There are different ways of talking about survival. These include

  • Disease free survival (DFS) – the percentage of people in the trial who are alive and cancer free after a specified number of years
  • Overall survival (OS) is the number of people alive, with or without signs of cancer
  • Median survival time is the length of time from either the diagnosis or the treatment of a disease, to the point at which half of the patients are still alive

Where to find out more about statistics

We have information about

Last reviewed

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

Find a trial

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