A study looking at why some breast cancers respond better than others to the drugs letrozole or anastrozole

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

Cancer type:

Breast cancer





This study is looking at blood and tissue samples to understand more about why the drugs letrozole (Femara) or anastrozole (Arimidex) help some people with breast cancer more than others.

Some people may have breast cancer that is too large or unsuitable for surgery. Or there may be a medical reason why surgery may not be the best first treatment. In these situations, if your breast cancer is oestrogen receptor positive Open a glossary item, your doctor may try to shrink the cancer before surgery, using drugs that lower the amount of the hormone Open a glossary item oestrogen in the body. We know from research that these drugs help most people.  In some people, the cancer responds, but in some cases only for a short time.  And in a few people, it doesn’t respond at all. Researchers want to work out why most people benefit but a few do not.

In this study, researchers will look at blood and tissue samples from people taking a type of hormone therapy called an aromatase inhibitor. The drugs they are looking at are called letrozole and anastrozole. They will test the samples to see whether the gene and protein changes that happen as a result of taking these drugs can be linked to how much the cancer shrinks. This will help them see if there is any way of predicting who will benefit from these drugs, and who might not.  

You will not get any direct benefit from taking part in such a study, and it is unlikely to change your treatment plan in any way. But the results of the study will be used to help other people with breast cancer in the future.

Who can enter

You may be able to enter this study if you

  • Are under the care of doctors at the Edinburgh Breast Unit
  • Have breast cancer that is sensitive to the hormone oestrogen (oestrogen receptor positive breast cancer)
  • Are due to start a type of hormone therapy called an aromatase inhibitor to shrink your tumour before surgery for breast cancer

You cannot enter this study if you

  • Have a rare type of breast cancer called inflammatory breast cancer
  • Have already had any treatment for breast cancer (including medication as part of another trial if there is any chance some of the drug could still be in your body)
  • Would be due to have radiotherapy, immunotherapy Open a glossary item or chemotherapy at the same time as taking part in this study
  • Have any other medical or mental health condition that would stop you taking part

Trial design

This study will recruit 500 people.

Everyone taking part will give 1 or 2 blood and tissue samples (biopsies). You have the first study biopsy at the same time as having a marker put into your breast that will guide the surgeon if and when you have surgery. This marker is not part of the study, and is put in place in case your treatment shrinks your cancer so much that the surgeon cannot feel it. You have the second biopsy 3 months later. The study team will also measure your breast cancer using an ultrasound scan.

By agreeing to take part, you are also giving the team permission to study tissue you had removed when you were diagnosed with breast cancer.

Hospital visits

You will visit the hospital to give your blood and have your biopsy

  • Two weeks after you start treatment
  • After 3 months of treatment, or during your surgery

Side effects

Your breast may be bruised and feel sore for a few days after your biopsy. You may also have a small bruise where you gave blood samples.

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 JM Dixon

Supported by

Breakthrough Breast Cancer
National Institute for Health Research Cancer Research Network (NCRN)
University of Edinburgh

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 8788

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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