A study looking at the drug metformin in breast cancer

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 the effect the diabetes Open a glossary item drug metformin has on breast cancer, in women due to have chemotherapy before surgery.

Cancers need food and oxygen to grow. But cancer cells seem to use these in different ways to healthy cells. Doctors call this ‘cancer metabolism’.

This study is looking at a drug called metformin, which doctors use to treat diabetes. We know from research that metformin can kill cancer cells, almost certainly because of how it affects cancer metabolism. We also know that metformin seems to help chemotherapy to work better in people with breast cancer who take it for diabetes. But we do not yet know if this is the case for people with breast cancer without diabetes.

Women taking part in this study will take metformin before, and possibly during, the chemotherapy they are having for their breast cancer. Researchers will look at scans, blood tests and biopsies from these women to gather information on how metformin affects cancer metabolism. They hope this study will help doctors predict which patients are most likely to respond well to this treatment in future.

Who can enter

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

You cannot enter this study if you

  • Have had any cancer treatment in the last 4 weeks, or you are due to have these when you would be taking part in the trial
  • Are taking medication as part of another clinical trial
  • Have had any severe injury or major surgery in the last 4 weeks
  • Have diabetes
  • Have a blood sugar reading of more than 7 mmol per litre – you can check this with your doctor
  • Have taken the drug metformin in the last year
  • Are sensitive to metformin
  • Have poor kidney function
  • Have a condition where the chemical balance of your blood becomes too acid (metabolic acidosis)
  • Are pregnant or breastfeeding
  • Have any other condition that would make you unwell if you took part, or affect the results of the trial – you can check this with your doctor

Trial design

This phase 2 study will recruit 40 women.

Everyone will take metformin every morning, for between 14 and 21 days.  You increase the dose after 3 days, then again after 3 more days if you do not have any side effects.

Everyone will also have a research PET-CT scan, breast biopsy and blood and urine tests before and after their course of metformin tablets.

A few days after your repeat scans, biopsies and blood and urine tests, you start the chemotherapy already planned for you, which is not part of the trial. The study team may ask you to carry on taking metformin until you finish your course of chemotherapy.

The evenings before your breast biopsies and blood and urine tests, the team will ask you to drink half a glass of some special water called deuterated water. The team will measure this out for you to take home.  You drink this water at 8pm and 10pm, and then have nothing to eat or drink until you have had the biopsies and blood and urine tests the next day. Deuterated water will help the team look at changes in breast cancer fats, caused by metformin.

You should not eat or drink anything for 12 hours before each of your PET-CT scans. You will need to drink lots of water just before your scan, and the team will tell you how much and when to do this.

Even though you will not be eating or drinking you must still take the metformin on the mornings of the second PET-CT scan and blood tests with a small amount of water.

The team will also ask permission to study any tissue samples you may have already had removed.

Hospital visits

Before you join the study, you will see the doctor and have a physical examination and some blood tests.

You may have your PET-CT scan on one day, followed by your study breast biopsy blood and urine samples the next. Or, you may have all these tests in one day.

Two or 3 weeks later you see the doctor and repeat the scans, biopsy and blood and urine samples in the same way as before.

The study team will refund travel expenses for you, and your carer if you have one.

Side effects

Side effects of metformin include

  • Taste changes
  • Feeling sick
  • Diarrhoea
  • Loss of appetite

Very rarely, people taking metformin can develop a serious condition called lactic acidosis. Symptoms of this are breathlessness, muscle cramps and tummy pain. This has mostly happened in people with kidney failure. You will have blood tests to make sure that your kidneys are working properly before you join the study. You should also stop taking metformin at least 2 days before any major surgery you have, including your breast surgery.

You will be exposed to some radiation from the study PET-CT scans. We are all exposed to a very small amount of radiation during the course of a normal day (background radiation). The amount of radiation you would have from each PET-CT scan is the same as 6 years of background radiation. Doctors think that in every 700 people who had these extra scans, 1 person would be likely to develop cancer as a result. The study team think that risk to you would be slightly less than this, as one of the study PET-CT scans will replace a CT scan you would have had if you were not taking part.

Deuterated water is safe and non toxic. But some people may feel dizzy for a few hours after drinking it.

You may have a small bruise where you gave your blood sample.

You may have some tenderness or bruising where you had your biopsy. If you have any bleeding, swelling, fever or pain that is not relieved with paracetamol, you should contact the study team straight away.

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 Adrian Harris

Supported by

Cancer Research UK
Engineering and Physical Sciences Research Council (EPSRC)
Experimental Cancer Medicine Centre (ECMC)
National Institute for Health Research Cancer Research Network (NCRN)
Oxford Cancer Imaging Centre
Oxford Centre for Diabetes
Endocrinology and Metabolism
Oxford Radcliffe Hospitals NHS Trust

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 7824

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Caroline took part in a clinical trial for breast cancer

“I had treatment last year and I want to give something back.”

Last reviewed:

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