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

Please note - this trial is no longer recruiting patients. We hope to add results when they are available.

Cancer type:

Breast cancer




Phase 2

This study is looking at a new drug called irosustat with other hormone therapies to treat breast cancer that has spread to the surrounding tissue (locally advanced Open a glossary item) or to another part of the body (secondary breast cancer). The trial is for post menopausal Open a glossary item women who have oestrogen receptor positive Open a glossary item (ER positive) breast cancer. This study is supported by Cancer Research UK.

Most breast cancers in post menopausal women need the hormone oestrogen Open a glossary item 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 think that by blocking both pathways the amount of oestrogen can be reduced further.

The aims of this trial are to see how well adding irosustat to an aromatase inhibitor works and how safe this combination is.

Who can enter

You may be able to enter this trial if you are a woman and

  • You have breast cancer that has tested positive for oestrogen receptors (ER positive)
  • Your breast cancer was locally advanced or had spread to another part of your body when diagnosed
  • Your first course of treatment when diagnosed was an aromatase inhibitor and your cancer responded or was stable for 6 months before it started to grow again
  • You are still taking aromatase inhibitors
  • Your cancer can be measured on a CT scan or MRI scan
  • Your periods have stopped (you are post menopausal)
  • You are well enough to be up and about for at least half the day (performance status 0, 1 or 2)
  • You have satisfactory blood tests results
  • You are at least 25 years old

You cannot enter this trial if you

  • Have HER2 positive breast cancer
  • Have had more than 1 course of chemotherapy to treat your advanced breast cancer
  • Have cancer that has spread to another part of the body and it is growing quickly or needs to be treated with chemotherapy
  • Are taking other hormone therapy as well as aromatase inhibitors
  • Have taken steroids for more than 2 weeks in the past month
  • Have had radiotherapy in the last 2 months to the area the doctors want to measure for this trial
  • Have had another cancer in the past 5 years, apart from successfully treated non melanoma skin cancer or carcinoma in situ Open a glossary item
  • Are having another experimental drug as part of another clinical trial
  • Are taking medications that could affect the way irosustat works in your body including medications that affect the CYP2C and CYP3A enzymes – your doctor can advise about this
  • Have an infection
  • Have a heart problem that is a cause for concern
  • Have any other medical condition that could affect you taking part in this trial

Trial design

This is a phase 2 trial. It will recruit 27 women. Everyone will have irosustat.

Irosustat is a tablet you take daily. You continue to have it as long it is helping you and the side effects aren’t too bad.  

If you agree to take part in this trial the researchers will ask your permission to take a piece of tissue from when you were first diagnosed. They want to analyse this sample to try and understand who may benefit from this treatment.

If you had a tissue sample (a biopsy) taken when your cancer came back or from your cancer spread, the researchers will also ask your permission to have a piece of this sample. If you didn’t, they will ask your permission to take a biopsy provided your doctor thinks it is safe to do so. You don’t have to agree to a biopsy if you don’t want to. You can still take part in the trial.

Hospital visits

You see the doctor to have some tests before starting treatment. These tests include

During treatment you see the doctor for a physical examination and blood tests. You have these monthly for 6 months and then every 3 months. You have a heart trace and scan every 3 months.

After stopping treatment, you see the doctor a month later for a physical examination, blood tests and heart trace.

Side effects

The most common side effects of irosustat are

Your doctor will talk to you about the possible side effects before you agree to take part in this trial.

We have information about the aromatase inhibitors letrozole, anastrozole and exemestane in our cancer drugs section.

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 Carlo Palmieri

Supported by

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

Other information

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

Questions about cancer? Contact our 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.

Harriet wanted to try new treatments

Picture of Harriet

“I was keen to go on a clinical trial. I wanted to try new cancer treatments and hopefully help future generations.”

Last reviewed:

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