Understanding the trial results

A clinical trial protocol should state clearly what sort of results the researchers need to collect to decide which treatment is most effective and safest. These are called outcomes or end points.

The first outcome that the researchers will be looking for in a phase 2 trial is how effective the treatment has been in treating the cancer. If the cancer has stopped growing, shrunk or disappeared it is known as a response.

A complete response to treatment is defined as the disappearance of all of the detectable cancer for at least four weeks. Clearly this is a very good result, but even a complete response does not mean a cure. It takes several years with no sign of recurrence before the cancer can be thought of as cured.

A partial response is a decrease in cancer size by at least half for at least four weeks, without any signs of growth elsewhere in the body.

Duration of response is the period of time between a response to treatment and any recurrence of the cancer, or the cancer starting to grow again (should that happen).

Progression means that the size of the cancer has increased by more than a quarter, or that new areas of cancer have appeared.

Time to progression is the length of time between starting treatment and the cancer progressing.

Stable disease means that a tumour is not getting any larger and the person’s medical condition is stable.

Progression-free survival measures the length of time until the cancer starts to develop or get larger again.

Having measured the immediate response to treatment, researchers then start to look at more long-term outcomes. In a phase 3 trial, the length of time people live after the treatment (survival) is usually the main outcome, and researchers will monitor whether more patients are cured, or live longer, with the new treatment.

Overall survival is obviously a very important outcome – it means how long patients live after they have entered the trial. This could be weeks, months or years, and takes account of all causes of death. Many cancer patients recover from their tumour and die from something quite different, years later. This will be recorded in the trial results. When cancer doctors talk about survival they usually measure this by looking at the number of people who have survived 5 or 10 years after their cancer was diagnosed. You may hear the terms ‘5-year survival’ or ’10-year survival’. Many people will live for much longer than this, but these figures are often quoted. This is because if someone has no sign of their cancer for five years after their treatment, it is unlikely to come back and he or she has a good chance of being cured.

Doctors will also be looking at how many side effects the treatment causes and how mild or severe they are. You may be asked lots of questions about side effects and might be asked to fill in questionnaires about any side effects that you have