A study looking at irosustat to treat advanced breast cancer (IRIS)

Cancer type:

Breast cancer




Phase 2

This study looked at a new drug called irosustat with another hormone therapy used to treat breast cancer called aromatase inhibitors Open a glossary item

It was for post menopausal Open a glossary item women whose cancer: 

  • had spread to the surrounding tissue (locally advanced) or to another part of the body (secondary breast cancer)
  • was oestrogen receptor positive Open a glossary item (ER positive) 

Cancer Research UK supported this study.

More about this trial

Most breast cancers in post menopausal women need the hormone oestrogen to grow. There are 2 pathways in the body that make oestrogen. 

Aromatase inhibitors are a type of hormone therapy that works by blocking one of these pathways. Irosustat is another type of hormone therapy that works by blocking the other pathway.  

The researchers thought that by blocking both pathways the amount of oestrogen could be reduced further.

The aims of this trial were to see how well adding irosustat to an aromatase inhibitor worked and how safe this combination was. 

Summary of results

The team found that adding irosustat to an aromatase inhibitor did work and was safe to use. 

This was a phase 2 study. 27 women took part. They had all had treatment with an aromatase inhibitor which had worked for some time but then their cancer had got worse. 

In this study they had irosustat with their aromatase inhibitor. Everyone had at least 1 dose of irosustat.

To find out if irosustat worked the researchers wanted to know how many women had:

  • no sign of their cancer (a complete response)
  • cancer that had shrunk (a partial response)
  • cancer that had stayed the same (stable disease) for a continuous period of 6 months 

They were able to assess 23 women. They found that 5 women had stable disease for at least 6 months. The average length of time that the disease remained stable disease was about 9½ months.

The most common side effects reported were:

  • dry skin
  • feeling sick
  • tiredness

The team concluded that there was evidence aromatase inhibitors and irosustat worked together when combined and was safe to use. But, more studies are needed to explore this further. 

We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) but may not have been published in a medical journal.  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

Professor Carlo Palmieri

Supported by

Cancer Research UK
Experimental Cancer Medicine Centre (ECMC)
National Institute for Health Research Cancer Research Network (NCRN)

Other information

This is Cancer Research UK trial number CRUK/11/025.

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

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 8278

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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