A study looking at the changes in the breast cancer of postmenopausal women having hormone therapy (Primary Endocrine Response Study)

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Cancer type:

Breast cancer




Phase 3

This study is looking at the early changes that occur in the breast cancer cells of postmenopausal women who are taking hormone therapy.

Postmenopausal women with large or locally advanced breast cancer that is oestrogen receptor (ER) positive may start their treatment with a type of hormone therapy called an aromatase inhibitor. Aromatase inhibitors are a group of drugs that work by blocking oestrogen made in the body.

In this study the researchers want to compare samples of breast cancer tissue, before and during hormone therapy, to see if there are changes in breast cancer cells.

The aims of this study are to

  • Find out what changes there are to breast cancer cells after 2 weeks of aromatase inhibitors
  • Find out if these changes can be used to predict the response of breast cancer to longer term treatment

Who can enter

You can enter this trial if you

You cannot enter this trial if you

  • Have breast cancer that has spread to another part of your body

Trial design

This phase 3 study will recruit women from the Edinburgh Breast Unit at the Western General Hospital, Edinburgh. To start with, 40 women will be recruited so that the researchers can look for changes in breast cancer cells. Another 40 women will then be recruited to test if these changes can be used to tell in advance how breast cancer may respond to aromatase inhibitor treatment.

In this study the researchers are using an aromatase inhibitor called letrozole. All women taking part in this study will take letrozole tablets for 3 months.

Hospital visits

You will see the doctor and have some tests before taking part in the study.

These tests include

After 2 weeks you have another biopsy.

During treatment you will see the doctor regularly and have a breast examination, mammogram and ultrasound.

Side effects

The most common side effects of letrozole are

You can find more about letrozole on CancerHelp UK.



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

Mike Dixon

Supported by

Experimental Cancer Medicine Centre (ECMC)
Lothian Health Board

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.

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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