A trial looking at the drug metformin for early breast cancer

You may be able to enter this trial if you are female and

• You have been diagnosed with breast cancer in the past year
• Your breast cancer is bigger than 1 cm and has grown into the surrounding tissue (stage T1c to T3)
• Your breast cancer has been tested for hormone receptors and HER 2 receptors
• You have had your sentinel lymph node removed or the lymph nodes under your arm removed
• You have satisfactory blood test results
• You are well enough to be up and about for at least half the day (performance status 0, 1 or 2)
• You and your partner are willing to use reliable contraception if there is any chance you could become pregnant
• You are 18 to 75 years old

You cannot enter this trial if

• Your breast cancer has spread to another part of your body
• You have breast cancer that has come back in the same area (local recurrence)
• You had cancer in more than 3 lymph nodes
• You have had chemotherapy in the past month
• You have had another cancer apart from non melanoma skin cancer or in situ carcinoma of the cervix that has been successfully treated or any other cancer that has been successfully treated and there has been no sign of it for the past 5 years
• You have diabetes
• You can’t have metformin
• You are already taking metformin, sulfonylureas, thiazolidenediones or insulin
• You have any other medical condition that could affect you taking part in this trial

This is an international phase 3 trial. It will recruit 3,580 women from different countries around the world. This is a randomised trial. The people taking part are put into 1 of 2 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 either. This is called a double blind trial.

The women in group 1 will have metformin for 5 years. The women in group 2 will have a dummy drug (placebo) for 5 years. Both metformin and the dummy drug are tablets. You take 1 tablet daily for 4 weeks. You then take 2 tablets a day, 1 in the morning and 1 tablet in the evening. You take your tablets with food.

If you agree to take part in this trial you will have 3 extra blood tests to measure how much sugar and insulin is in your blood (a fasting blood test). Before these blood tests you must not eat or drink anything other than water for 12 hours.

If you agree to take part in this study, the researchers will ask for a sample of tissue taken from when you had surgery to remove your cancer. If you don’t want to give tissue samples for this study, you don’t have to. You can still take part in the trial.

You see the doctor before taking part in this trial and have some tests. These tests may include

• A physical examination
• Mammogram
• Chest X-ray
• CT scan
• Liver ultrasound
• Bone scan
• Blood tests including a fasting blood test

During treatment you see the doctor after 6 months, 1 year and then once a year after that.  You have a physical examination and blood tests at each appointment. You have a fasting blood test at 6 months and 5 years. You have a mammogram every year.  

The most common side effects of metformin are

• Diarrhoea
• Feeling or being sick
• Tummy (abdominal) bloating
• Wind (flatulence)
• Loss of appetite