A trial looking at a new drug called giredestrant (GDC-9545) for breast cancer (acelERA Breast Cancer)

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

Cancer type:

Breast cancer
Secondary cancers




Phase 2

This trial is for people with breast cancer that has either:

  • spread into the area around the breast (locally advanced) and has come back or got worse after treatment or
  • spread to other parts of the body (secondary, metastatic or advanced)

It is for people whose breast cancer cells are sensitive to the hormone oestrogen (oestrogen receptor positive or ER positive). And whose breast cancer does not have receptors for a protein called HER2 (HER2 negative).

More about this trial

Hormone therapy is a common treatment for locally advanced or secondary breast cancer.

Many breast cancers need the hormone oestrogen to grow. These are called oestrogen receptor positive breast cancers. Doctors think that giredestrant (GDC-9545) might stop oestrogen getting to the cancer cells. It stops growth by blocking oestrogen receptors.

The trial team want to find out if giredestrant works better than hormone therapy drugs we already have. To do this, everyone in this trial will either have giredestrant or another hormone therapy drug. 

Your doctor will choose the most suitable hormone treatment for you if you are not having giredestrant. This will either be fulvestrant or an aromatase inhibitor Open a glossary item.

The aims of this trial are to find out:

  • if giredestrant works better than other hormone treatments such as fulvestrant or an aromatase inhibitor
  • how safe the treatment is
  • more about the side effects
  • more about quality of life

Who can enter

The following bullet points are a summary of the entry conditions for this trial. Talk to your doctor or the trial team if you are unsure about any of these. They will be able to advise you. 

Who can take part

You may be able to join this trial if all of the following apply. You:

  • have locally advanced Open a glossary item adenocarcinoma Open a glossary item of the breast (breast cancer) or adenocarcinoma of the breast that has spread to another part of the body (advanced, secondary or metastatic)
  • have cancer that is sensitive to the hormone oestrogen (ER positive) and does not have receptors for the HER2 protein (HER2 negative)
  • have cancer that the doctor can measure on a scan
  • have had 1 or 2 different cancer drug treatments for advanced Open a glossary item or secondary breast cancer. One of these must have been a hormone therapy which you had for at least 6 months before your cancer started to grow again. Your doctor can tell you more.
  • are unable to have more treatment that doctors think will cure your cancer
  • have a sample of tissue (biopsy) available that the trial team can do some tests on or you are willing to give a new sample
  • have satisfactory blood tests results
  • are post menopausal Open a glossary item, or you are willing to take a drug that stop the ovaries from making hormones (LH blocker Open a glossary item) for the time you are in the study, if you are female
  • are willing to take a drug to block the oestrogen in your body (LH blocker), for the time you are in the study, if you are male
  • have recovered from the side effects of any treatment you have had before, apart from if you still have some hair loss or mild peripheral neuropathy Open a glossary item
  • are willing to use reliable contraception, that is not hormonal, during treatment if there is any chance you or your partner could become pregnant, how long you must continue this for depends on which drugs you take during the trial
  • are willing to not donate eggs or sperm during treatment, how long you must continue this for depends on which drugs you receive during the trial
  • are well enough to carry out all your normal activities, apart from heavy physical work (performance status of 0 or 1)
  • are well enough to have hormone therapy
  • are expected to live longer than 6 months
  • are at least 18 years old
  • are able to use an electronic device to record how you are feeling and any side effects that you are having

Who can’t take part

Cancer related

You cannot join this trial if any of these apply. You:

  • have cancer that has spread to places which are life threatening in the short term, for example you have a very large amount of fluid around the lung (pleural effusion)
  • have cancer that has spread to the brain or the spinal cord which is causing you symptoms or that is not able to be controlled with treatment – you might be able to take part if you have cancer that has spread to the brain or have spinal cord compression and you don’t have symptoms or have not had treatment with steroids or anti epilepsy medicines in the last 2 weeks before randomisation Open a glossary item
  • have had another cancer within the past 5 years before you have the tests to see if you’re able to join the trial - apart from treated non melanoma skin cancer Open a glossary item, cervical carcinoma in situ Open a glossary item, or early (stage 1) womb cancer
  • have had drugs that affect oestrogen in a similar way to giredestrant before, your doctor can explain more. You can take part if you have had fulvestrant and stopped taking it at least 28 days before randomisation.
  • have had more than one treatment course that included chemotherapy Open a glossary item after your cancer had come back, or got worse, with treatment
  • have had more than one targeted cancer drug Open a glossary item course after your cancer had come back, or got worse, with treatment
  • have had major surgery, chemotherapy, radiotherapy or other anti cancer treatment within 14 days before randomisation
  • have had any trial or study drugs in the last 28 days before randomisation
  • are expected to have major surgery during the time you would be taking part in the trial

Medical conditions
You cannot join this trial if any of these apply. You:

  • have HIV
  • have liver disease, including active viral hepatitis or hepatitis B or hepatitis C or currently have liver scar tissue (cirrhosis), or you are drinking too much alcohol at the moment
  • have a serious heart problem such as a heart attack within the last 12 months or other heart problems, such as a slow heart rate. The trial team check if you have a heart condition before you join the trial.
  • have bowel problems which might make it difficult to absorb the study drugs, this includes inflammatory bowel disease, long term diarrhoea, short bowel syndrome or have had major food pipe, stomach or upper bowel surgery
  • have had a serious infection which needed antibiotics within 14 days before randomisation
  • have any other serious medical condition that the trial team think could affect you taking part


You cannot join this trial if any of these apply. You:

  • have not had the menopause yet and unable or don’t want to take LH blockers, or are male and are allergic to LH blockers
  • are pregnant or breastfeeding, or intending to become pregnant just after the study
  • are allergic to any of the study drugs or anything they contain

Trial design

This is a phase 2 trial. The researchers hope 300 people will take part worldwide, including 20 from the UK.

The trial is split into 3 stages:

  • screening stage – the trial team makes sure you are able to take part in the trial
  • treatment stage
  • follow up – this is to check how you are getting on after the trial 

It is a randomised trial. You are put into one of the following treatment groups by computer:

  • Group 1– you have giredestrant
  • Group 2 – you have the hormone therapy your doctor has chosen for you

Both you and your doctor know which group you are in.

Group 1 (giredestrant)
You have giredestrant as a tablet once a day for 28 days. This is one cycle of treatment.

Group 2 (other hormone therapy)
How you have your hormone therapy depends on the drug. You might have it as a tablet or as an injection. Your doctor will explain how and how often, you have the drug.

Everyone who is pre menopausal, or male, will also have a LH blocker. This is to try and block sex hormone production in your body. You usually have this once every treatment cycle.

You will have treatment for as long as it is working, and you can cope with any side effects. This could be for more than 20 months.

Quality of life

The trial team will ask you to fill out questionnaire:

  • before you start treatment
  • at set times during treatment 
  • after you finish treatment

The questionnaires will ask about side effects and how you’ve been feeling. This is called a quality of life study.

Samples for research

The trial team will ask you to give some extra blood samples. Where possible you have these at the same time as your routine samples. 
They will ask to look at a sample of tissue you gave when you were first diagnosed. 
The researchers plan to look at:

  • substances called biomarkers Open a glossary item to help work out why treatment might work for some people and not for others
  • what happens to the drugs in your body
  • genes Open a glossary item to learn more about breast cancer

They might also ask you to give a new sample if your cancer gets worse. You don’t have to agree to this. You can still take part in the trial and will not affect your care.

Hospital visits

You see a doctor and have some tests before you can take part. These include:

  • a physical examination
  • heart trace (ECG)
  • urine sample, including pregnancy test (if you are able to become pregnant)
  • blood tests
  • a biopsy Open a glossary item so the study doctors can look at the tumour tissue – if a good enough sample is available already, the team will use this
  • heart scan, such as an ECHO Open a glossary item or MUGA Open a glossary item
  • scans to look at a larger area of your body, or your whole body such as a CT scan, MRI scan or bone scan

Hospital visits during treatment

You go to the hospital to see the trial team about once a month. Each treatment visit takes around 1 to 6 hours. At each visit, you see the trial doctor for a check up and blood tests.

Depending on the treatment you have, you might record the study treatment you take in a diary at home.

Scans during treatment

You have a CT or MRI scan about:

  • every 8 weeks for the first 18 months
  • every 12 weeks after the first 18 months

You have a bone scan around every 24 weeks.

After you have finished treatment you see your trial doctor:

  • after 30 days
  • after 3 months

After that, the trial team will catch up with you at least every 6 months for as long as you are willing to see them.

Side effects

The trial team monitor you during treatment and afterwards. Contact your advice line or tell your doctor or nurse if any side effects are bad or not getting better.

Giredestrant is a new drug. There may be side effects we don’t know about yet. Possible side effects of giredestrant include:

  • blood clots
  • kidney changes
  • liver changes
  • changes to female reproductive organs – such as fluid filled sacs on the ovaries (cysts) and changes the womb
  • feeling or being sick
  • slow heartbeat
  • inability to get pregnant, or get your partner pregnant
  • menopausal symptoms such as loss of muscle and bone, hot flushes, vaginal dryness or discharge, irritation, mood swings and less interest in sex
  • problems with a developing baby, or miscarriage

Side effects of hormone therapy for breast cancer include:

  • hot flushes and sweating
  • changes to your periods if you are pre menopausal
  • less interest in sex
  • vaginal dryness or discharge
  • feeling sick
  • painful joints
  • mood changes
  • tiredness

A side effect of aromatase inhibitors is bone thinning (osteoporosis) or weakening.

We have more information about hormone therapy for breast cancer. We have more detailed information on fulvestrant, or choose your hormone therapy drug from our A-Z list.

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

Dr Sarah Khan

Supported by


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.

Over 60,000 cancer patients enrolled on clinical trials in the UK last year.

Last reviewed:

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