A trial of abiraterone for breast cancer that has spread

Cancer type:

Breast cancer




Phase 1/2

This trial looked at abiraterone for breast cancer that has spread and is oestrogen receptor positive or androgen receptor positive. It was supported by Cancer Research UK.

More about this trial

Some breast cancer cells have oestrogen receptors on the surface. This is called oestrogen receptor positive (ER positive) breast cancer. The hormone oestrogen attaches to the receptors and encourages the cancer to grow. Hormone therapy can stop this happening and so helps stop the cancer growing.
Some breast cancer cells also have androgen receptors. Androgen receptors are similar, but triggered by hormones called androgens. This is called AR positive breast cancer. 
Abiraterone (CB7630 or Zytiga) blocks an enzyme called cytochrome P17, or CYP17. Blocking CYP17 helps stop the body making hormones, including androgens and oestrogen. 
When this trial was done, abiraterone had already been looked at in trials for prostate cancer. It lowered androgen levels and helped slow down the growth of or shrink prostate cancers. Researchers hoped it would have the same effect on ER and AR positive breast cancer.
In this trial, the researchers wanted to see if abiraterone helps women who have breast cancer that is not responding to standard treatments.
The aims of the trial were to find out:
  • the best dose of abiraterone to give
  • what happens to abiraterone in the body
  • how well it works for breast cancer
  • what the side effects are

Summary of results

The research team found that abiraterone didn’t work as well as they’d hoped for breast cancer that has spread.
This trial was open for people to join between 2008 and 2014, and the team reported results in 2016.
About this trial
There were two parts (phases) in this trial.
In phase 1, the first few people had the lowest dose of abiraterone. As they didn’t have any serious side effects, the next few people had a higher dose. And so on, until they found the best dose to use. This is called dose escalation. 
In phase 2, everyone had the same dose of abiraterone. The dose they had 
was based on the results from phase 1.
Everyone taking part had abiraterone tablets once a day. How long they had treatment depended on their individual situation.
This trial recruited 75 women with advanced breast cancer. They had all been through the menopause and had cancer that was oestrogen receptor (ER) positive, androgen receptor (AR) positive, or ER and AR positive. 
There were:
  • 25 women in phase 1
  • 50 women in phase 2
The trial team looked at how well treatment worked for the 58 women who had treatment for at least 8 weeks.
They found that out of 18 people in phase 1, the cancer had:
  • got a bit smaller in 1 person (5%)
  • stayed the same in 5 people (28%)
  • continued to grow in 12 people (67%)
They found that out of 40 women in phase 2, the cancer had:
  • not got smaller in anyone
  • stayed the same in 25 people (62%)
  • continued to grow in 15 people (38%)
They looked at how many women who took part in phase 2 were living 2 years after treatment. They found it was 11 out of 50 women (22%). 
They compared the results for women who had receptor positive and receptor negative cancer, and found there wasn’t much difference. The research team didn’t feel these results were good enough to recommend abiraterone was looked at in further trials.
Side effects
About 4 out of 5 women (81%) who took part had at least one side effect. But many were mild or didn’t last long. 
The most common side effect was low levels of blood potassium (hypokalaemia). This can be serious if not treated, but it usually goes back to normal levels with treatments such as potassium supplements.
Other side effects included:
  • tiredness (fatigue)
  • feeling or being sick
  • constipation
  • pain
  • shortness of breath or cough
  • swelling in legs or feet (oedema)
  • an increased risk of infection
We have more information about the side effects of abiraterone in our Cancer Drugs section.
The research team concluded that abiraterone did have some effect on breast cancer that had spread. But it didn’t work well enough for them to recommend that it’s looked at in further trials. 
Even when a trial shows a treatment isn’t useful for a particular cancer, it adds to our knowledge and understanding. All trial results help doctors and researchers learn more about different cancers and the best way to treat them. 
Where this information comes from
We have based this summary on information from the research team.  As far as we are aware, the information they sent us has not been reviewed independently (peer reviewed Open a glossary item) or published in a medical journal yet. The figures we quote above were provided by the research team. We have not analysed the data ourselves.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

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

Chief Investigator

Prof Johann de Bono

Supported by

Cancer Research UK (Centre for Drug Development)
Cougar Biotechnology
Experimental Cancer Medicine Centre (ECMC)
NIHR Clinical Research Network: Cancer

Other information

This is Cancer Research UK trial number CRUKD/08/044.

If you have questions about the trial please contact our cancer information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:


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

Last reviewed:

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