A trial looking at metformin for early breast cancer (MA32)

Cancer type:

Breast cancer

Status:

Results

Phase:

Phase 3

This trial looked at adding metformin to standard treatment Open a glossary item for early breast cancer . It was for women who had already had surgery to remove the cancer and had a higher risk of it coming back.

The trial was open for women to join between 2010 and 2013. The team published the results in 2022.

Cancer Research UK supported this trial.

More about this trial

Metformin is a treatment for type 2 diabetes Open a glossary item . It works by lowering blood levels of a hormone called insulin .

When this trial was done, researchers knew that people with breast cancer who have low insulin may do better than those with high levels. They also knew that metformin might help to slow breast cancer from spreading.

Researchers wanted to find out more about how metformin works for breast cancer. So they did this trial to find out more.

Everyone had the standard cancer treatment their doctor thought best for them. For example, chemotherapy or radiotherapy, and:

half had metformin
half had a dummy drug (placebo )

Most people in the trial had breast cancer that had receptors for oestrogen Open a glossary item or progesterone . This is hormone receptor positive cancer. Some had cancer that didn’t have these receptors. This is hormone receptor negative cancer.

The aim of this trial was to find out if metformin improves treatment for early breast cancer.

Summary of results

3,649 people took part in this phase 3 trial Open a glossary item . They were put into a treatment group at random:

1,824 had metformin
1,825 had a dummy drug

The plan was for everyone to have metformin or the dummy drug for up to 5 years.

The researchers did an early analysis of the results in 2016. They found that metformin wasn’t helping women whose cancer was hormone receptor negative. So this group stopped having treatment as part of this trial.

Final results
The team had the results for 2,533 people. They all had breast cancer that was positive for hormone receptors. The team followed them up for about 8 years.

They looked at:

the length of time that people had no signs of cancer after their treatment
how long people lived

They found no difference between the 2 treatment groups in either of these.

Side effects
Most people had at least 1 side effect from treatment. But some of these were mild or didn’t last long.

Some people had more severe side effects. This was:

391 out of 1,824 people (21.5%) in the metformin group
328 out of 1,825 people (17%) in the dummy drug group

The severe side effects of metformin and the dummy drug included:

high blood pressure
irregular periods
diarrhoea

These side effects were worse in people who had metformin.

Conclusion
The team found that adding metformin to standard treatment didn’t stop breast cancer from coming back or getting worse. This was compared to those who had the dummy drug.

Sometimes trials show a different treatment isn’t useful for a particular type or stage of cancer Open a glossary item . But these trials still add to our knowledge and understanding of cancer and how to treat it.

More detailed information
There is more information about this research in the reference below.

Please note, the information we link to here is not in plain English. It has been written for healthcare professionals and researchers.

Effect of Metformin vs Placebo on Invasive Disease–Free Survival in Patients With Breast Cancer The MA.32 Randomized Clinical Trial
P Goodwin and others
JAMA, 2022. Volume 327, issue 20. Pages:1963-1973

Where this information comes from
We have based this summary on the information in the article above. This has been reviewed by independent specialists (peer reviewed Open a glossary item ) and published in a medical journal. We have not analysed the data ourselves. As far as we are aware, the link we list above is active and the article is free and available to view.