A study to learn more about how drugs that switch off oestrogen affect breast cancer cells (FemarA)

Cancer type:

Breast cancer




Phase 3

This study looked at tissue samples to compare the effects of drugs called anastrozole (Arimidex) and letrozole (Femara) on breast cancer cells.

Anastrozole and letrozole are both aromatase inhibitors. These are a type of hormone therapy that doctors often prescribe for women with breast cancer who have been though the menopause. They stop your body making the female hormone oestrogen, which can encourage breast cancer cells to grow.

This study was to learn more about the effects of letrozole and anastrozole on cancer cells. The women taking part had either letrozole or anastrozole for 2 weeks before their planned breast cancer surgery.

The researchers studied breast tissue that had been removed when the women had a biopsy to diagnose breast cancer, and compared them with tissue removed during surgery. They looked at how the drug affected the cancer cells and healthy breast tissue. They then compared the results from each drug.

The aim of this study was to see how each drug affected the growth of breast cancer cells.

Summary of results

The study team found there was no difference between anastrozole and letrozole.

This was a phase 3 study. It recruited 206 women.

The researchers were able to look at 209 tissue samples

  • 103 from the women who had anastrozole (2 of the women had cancer in both breasts)
  • 106 from those who had letrozole (1 woman had cancer in both breasts)

The researchers looked at the levels of substances (biomarkers) in the tissue samples that show how well treatment had worked. They compared the levels of the biomarkers before having 2 weeks of anastrozole or letrozole with the levels after treatment.

They then compared the results between anastrozole and letrozole. They found no significant difference between the 2 drugs.

The researchers also looked at how anastrozole and letrozole affected the growth of breast cancer cells that had receptors for the hormones oestrogen and progesterone. They found that both drugs had a major and rapid affect on the growth of cancer cells that had oestrogen receptors. But neither drug had much of an effect on cancer cells that had progesterone receptors.

The trial team concluded that there was no difference between anastrozole and letrozole.

We have based this summary on information from the team who ran the trial. The information they sent us has been reviewed by independent specialists (peer reviewed) and published in a medical journal. The figures we quote above were provided by the trial 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 JM Dixon

Supported by

Experimental Cancer Medicine Centre (ECMC)

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 4373

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

A 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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