A study looking at the drug metformin in breast cancer

Cancer type:

Breast cancer




Phase 2

This study looked at the effect the diabetes drug metformin has on breast cancer cells, in women due to have chemotherapy and then surgery.

More about this trial

Our cells process food and oxygen in a series of chemical reactions, so they can grow and develop. This is called metabolism. Cancer cells sometimes process food and oxygen differently to healthy cells. This is called cancer metabolism. 
This study looked at a drug called metformin, which is a treatment for diabetes Open a glossary item. Research had already suggested that metformin may prevent breast cancer developing in patients who already take it for their diabetes. But researchers wanted to find out if it could help people who already have breast cancer.
The women taking part in this study had recently been diagnosed with breast cancer. They were due to have chemotherapy and then surgery to remove the cancer. Everyone taking part had metformin for between 13 and 21 days before they started chemotherapy. 
The research team looked at PET-CT scans, blood tests and biopsies to find out more about what affect metformin has on cancer cells and cancer metabolism. 
The main aim of this study was to find out more about how metformin affects the metabolism of breast cancer cells.

Summary of results

The research team found that metformin did affect the metabolism of breast cancer cells in people who don’t have diabetes.

They recruited people between 2011 and 2013, and reported the results in 2018.

This study recruited 40 women who were due to have chemotherapy and surgery for newly diagnosed breast cancer. 

They took metformin tablets once a day for between 13 and 21 days before they started chemotherapy. They also had a PET-CT scan, blood tests and a biopsy before and after the course of metformin.

The research team found there were two main types of response to metformin.

FDG responders
Just under 8 out 10 people (78%) were what they called FDG responders. FDG is a mildly radioactive marker that doctors use to look at the metabolism of cells on a PET-CT scan. 

The scans of people in this group showed the amount of FDG taken up by the cancer cells increased after they took metformin. It’s likely that the metformin caused the cancer cells to change the way their metabolism works. 

These patients were also more likely to have a decrease in the level of a particular genetic marker. This suggests their breast cancer cells may grow more slowly after treatment with metformin. 

OXPHOS responders
Just over 2 out of 10 people (22%) were what they called OXPHOS responders. This means that there were extra copies of certain genes in the women’s cancer cells after they took metformin. 

These OXPHOS genes are involved with part of the cell called the mitochondria and with helping cancer cells grow. Mitochondria produce the energy that cells need to grow and survive. They are sometimes called ‘the energy powerhouses of cells’. 

Metformin may be less likely to work on cancer cells which have extra copies of these genes after treatment. In other words, the cells may be resistant to metformin.

Growth of cancer cells
Other studies had shown that metformin can reduce the growth of cancer cells. But the results of this study showed that there wasn’t much change.

They did find that people classed as OXPHOS responders had an increased number of certain genes involved with cell growth. There were less of these genes in some people who were FDG responders.

The research team concluded that it was likely that metformin does change the metabolism of breast cancer cells in some people. They suggest that more trials are done to find out if metformin could be a useful treatment for breast cancer. 

Researchers also want to find out whether there are specific genes that could tell us which breast cancer patients are more likely to respond to metformin.

Where this information came from
We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) and published in a medical journal. The figures we quote above were provided by the trial team who did the research. 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 Adrian Harris

Supported by

Breast Cancer Research Foundation
Cancer Research UK
Engineering and Physical Sciences Research Council (EPSRC)
Experimental Cancer Medicine Centre (ECMC) 
Medical Research Council (MRC)
NIHR Oxford Biomedical Research Centre
Oxford Cancer Imaging Centre
Oxford Radcliffe Hospitals NHS Trust

Other information

We have more information about the work of Professor Adrian Harris.

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.

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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