Abiraterone for prostate cancer

This page tells you about abiraterone, a new drug being developed for prostate cancer. You can find information about

• What abiraterone acetate is
• Research into abiraterone
• Is abiraterone available in the UK?

Abiraterone is a new hormone therapy drug that researchers are looking into for prostate cancer. It is also called CB7630 or abiraterone acetate. It works in a different way to other hormone treatments for prostate cancer.

The male hormone testosterone stimulates prostate cancers to grow. Stopping the body making testosterone can slow the growth of the cancer, or even shrink it. Most testosterone is made by the testes but a small amount is made by other tissue in the body including the cancer itself. To make testosterone the body needs an enzyme called cytochrome P17 (CYP17). Abiraterone acetate blocks this enzyme, which stops both the testes and other tissues in the body making testosterone.

Researchers are looking at using abiraterone treatment for men with prostate cancer that has spread to another part of the body, and who have had hormone therapy that is no longer working.

Abiraterone is still being looked at in clinical trials. The results from a phase 1 trial were published in July 2008 in the Journal of Clinical Oncology. There were only 21 men in this trial. All the men had prostate cancer that had spread and were taking hormone therapy, but it was no longer working. The men started taking abiraterone acetate once a day.

When the men started taking abiraterone, most of them (80%) had a fall in the level of prostate specific antigen (PSA) in their blood and their tumours shrank. A fall in PSA level usually means that the number of cancer cells has gone down. Some of the men who had pain were able to take lower doses of painkillers. The reduction in PSA level lasted from just over 2 months in some men to up to 18 months in other men.

Side effects were generally mild but included

• A change in the level of sodium and potassium in the blood
• A build up of fluid in the ankles (oedema)
• A rise in blood pressure
• Headaches
• Loss of appetite
• Fatigue
• Hot flushes

The researchers then carried out a phase 2 trial and the results were published in the Journal of Clinical Oncology in May 2009. The trial included 54 men all together. All the men had been having hormone therapy, but it was no longer working. In the trial, they started taking abiraterone and when abiraterone was no longer working, the men started taking a steroid called dexamethasone as well.

When the men were taking abiraterone alone, most had a fall in their PSA levels. This meant that the treatment was stopping the cancer from growing or developing. In just over a third of the men (37%) whose tumours could be measured on a scan, the cancer got smaller. And the PSA level went down by at least a half in about two thirds of the men (67%) taking part. After some time though the men’s PSA level started to rise again.

When this happened, the men could start taking dexamethasone as well as abiraterone. When the results were published in May 2009, 39 of the men had taken both drugs together. In some of these men, the level of PSA went down again, but levels started to rise once more after a few months. It is encouraging that the two drugs seemed able to lower the PSA once more. But do remember, these results are only for a very small number of men. So we will need more research with larger trials to confirm them.

Another phase 2 trial recently finished and the results have not yet been published but were discussed at a conference in America (ASCO) in 2008. Men in the trial had already had hormone treatment and chemotherapy called docetaxel for prostate cancer that had spread. When the men started taking abiraterone, nearly three quarters (75%) had a fall in their level of PSA. So, these early results look promising. In this trial, 14 of the men had secondary cancer in their bones. After 12 weeks of abiraterone treatment their cancer had not grown or developed.

From these studies, it looks as though abiraterone may help to control advanced prostate cancer for a time in some men. At the moment though, the studies have been on a small number of men with very advanced disease. So it is too early to say exactly how helpful this drug may be in treating men with earlier stage prostate cancer. Larger studies are planned.

Abiraterone is only available to men who take part in a clinical trial. A phase 3 trial called COU-AA-301 started in May 2008. It stopped recruiting patients in April 2009.

The aim of the trial is to find out how well abiraterone works. It is a randomised trial. The men taking part were put into treatment groups by a computer.

One group will have abiraterone once a day and a steroid called prednisolone twice a day. The other group will take a dummy (placebo) tablet once a day and prednisolone twice a day. The men taking part and their doctors will not know if they are taking abiraterone or the dummy tablet. They will carry on taking the treatment until it is no longer working.

Results from this trial won’t be available for at least a couple of years and the results will affect whether abiraterone acetate becomes more widely available.