Phase 3 clinical trials
If the results of phase 2 trials show that the new treatment is shows promise for treating cancer, it will be tested in phase 3 trials.
A phase 3 trial directly compares the new treatment with standard treatments to see if the new treatment is better.
The treatment is given to very large groups of people. Sometimes it involves thousands of patients in many different hospitals and even different countries. The larger the number of people in the trial (called the ‘cohort’), the more confident we can be about the results will be.
A phase 3 trial is usually ‘randomised’. This means the researchers use a computer to allocate the patients taking part into two or more groups. One group gets the standard treatment and the other groups get the new treatment, or a combination of the new treatment and the standard treatment.
At the end of the study the results for the groups are compared to see if they are different and if the new treatment is better.
Randomisation helps to make sure that it is the treatment being tested — and not other factors — that is responsible for the study results. Factors like whether a person is male or female, their age, ethnic background or diet can change how they respond to the treatment.
How advanced a person's cancer is or more subtle differences between each individual's cancer can also affect the response to treatment. If factors such as these aren’t taken into account, the information collected by the researchers will be misleading.
If a treatment passes the phase 3 trial, doctors will be allowed to give it to patients once it has been licensed by the Government.
Here’s an example of a phase 3 clinical trial:
A large phase 3 clinical trial, called ATAC (Arimidex, Tamoxifen Alone or in Combination), has recently shown that the drug anastrozole is more effective than tamoxifen for treating early-stage hormone-sensitive breast cancer.
This international trial, involving Cancer Research UK scientists in London, compared women with early breast cancer taking tamoxifen with those taking anastrozole. It involved over 9,000 post-menopausal women with this disease from all over the world.
After these women had surgery for their breast cancer, they were asked to take either:
- tamoxifen for 5 years
- anastrozole for 5 years, or
- a combination of tamoxifen and anastrozole
The trial showed that anastrozole alone was more likely to stop breast cancer coming back than tamoxifen alone, or the two drugs in combination.
Women with cancer in one breast are more likely to get cancer in the other breast, known as controlateral cancer. But anastrozole reduced the chances of developing cancer in the remaining breast by 80 per cent, whereas tamoxifen only reduced this risk by 50 per cent.
So, the trial also showed that anastrozole could be as effective at preventing breast cancer as treating it. Cancer Research UK-funded scientists are now leading a new trial, called IBIS II, which will investigate the preventative role of anastrozole further.
If you want to find out even more about phase 3 clinical trials, have a look at the ‘Understanding clinical trials’ section of our CancerHelp UK website. Information about trials that are currently open for recruitment can be found on the clinical trials database on CancerHelp UK.
