A trial looking at metformin for early prostate cancer (METAL)

Cancer type:

Prostate cancer




Phase 4

This trial is looking at using a drug called metformin for early prostate cancer. It is open to men with newly diagnosed prostate cancer that is contained within the prostate (localised) and who are going to have surgery to remove the prostate.

More about this trial

Doctors can treat localised prostate cancer by removing the prostate gland with surgery. After surgery you may have radiotherapy and hormone therapy. This works but unfortunately your cancer may come back. So researchers are always looking for other treatments.

Metformin is a drug used to treat diabetes Open a glossary item. Diabetes is part of a group of conditions called metabolic syndrome. Recent studies have suggested that having metabolic syndrome, or some features of it, may increase the risk of getting prostate cancer. Researchers think that metformin may reduce the risk of getting prostate cancer or may even be able to treat it. But before finding this out they need to know how and why metformin affects prostate cancer.

In this trial some men will have metformin before having surgery to remove their prostate and the other men will have a dummy drug (placebo Open a glossary item). The team will compare the tissue samples of these men taken when they are first diagnosed and then when the prostate is removed.

The trial team will also do a small sub study using a PET scan with an MRI scan (called a PET-MRI scan). They will compare a scan before starting metformin with another before surgery.

The aim of this trial is to find more about how and why metformin may affect prostate cancer.

Who can enter

You may be able to join this trial if all of the following apply

  • You have a type of prostate cancer called adenocarcinoma Open a glossary item
  • Your cancer is bigger than 6mm in length (your doctor can tell you this)
  • You are due to have surgery to remove your prostate
  • You have satisfactory blood test results
  • You are well enough to carry out all your normal activities, apart from heavy physical work (performance status of 0 or 1)
  • You are able to swallow capsules or tablets
  • You are willing to use reliable contraception during treatment and for 16 weeks afterwards if there is any chance your partner could become pregnant
  • You are at least 18 years old

You cannot join this trial if any of these apply. You

  • Have already had treatment for your prostate cancer
  • Have diabetes
  • Have at any time had metformin
  • Have had another cancer in the past 5 years that needed systemic treatment Open a glossary item apart from non melanoma skin cancer Open a glossary item or early stage transitional cell Open a glossary item cancers. If the aim of your main treatment, such as surgery, was to cure your cancer and you had systemic treatment after the main treatment you may be able to take part
  • Have, or had, a medical condition called lactic acidosis or another condition that is associated with it (your doctor can advise you about this)
  • Have certain heart problems (the trial doctor can advise about this)
  • Have an ongoing problem with your liver
  • Have any other medical or mental health problem that the trial team think could affect you taking part in the trial
  • Are currently taking part in another clinical trial using an experimental drug or device or have taken part in one in the past month
  • Are allergic to any of the drugs, or their ingredients, used in this trial

Trial design

This is a phase 4 trial. The researchers need a total of 105 men to join, 100 to join the main trial and 5 men to join the sub study.

The main part of the trial is randomised. The men taking part are put into treatment groups by a computer. Neither you nor your doctor will be able to decide which group you are in.  And neither of you will know which group you are in. This is called a double blind trial.

  • Men in one group have metformin
  • Men in the other group have a dummy drug (placebo)

METAL trial diagram

Metformin and the dummy drug are tablets. You take them until the evening before your surgery is due. Your doctor will tell you how many tablets to take and how often.

The 5 men who take part in the sub study will have metformin. As part of the sub study you have 2 PET-MRI scans. You have 1 scan before you start metformin. You have the other scan about 3 weeks later before you have surgery to remove you prostate. You cannot eat or drink, apart from water, for 4 hours before each scan.

The researchers will ask for a sample of your cancer from the biopsy Open a glossary item when you were diagnosed. They will also take another sample of tissue from your prostate after the surgery to remove it.


Hospital visits

You see the doctor to have a physical examination and blood tests

  • Before taking part
  • Twice before surgery
  • 8 – 10 weeks after surgery

Men in the sub study will have the PET-MRI scan before they start metformin and about a week before surgery.

Side effects

The most common side effects of metformin are stomach upset and diarrhoea.

The trial doctor will talk to you about the possible side effects before you agree to take part.



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

Dr Sarah Rudman

Supported by

Guy's and St Thomas' NHS Foundation Trust
J P Moulton Charitable Foundation
King's College London
NIHR Clinical Research Network: Cancer
Penguins Against Cancer

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.

Keith took part in a trial looking into hormone therapy

A picture of Keith

"Health wise I am feeling great. I am a big supporter of trials - it allows new treatments and drugs to be brought in.”

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