A low-cost diabetes drug could be used to treat patients with breast cancer, scientists have found.

Researchers at the University of Manchester in the UK and Thomas Jefferson University in the US have developed a test to identify patients who could benefit from metformin, a standard treatment for type 2 diabetes valued at 10p.

They found that if cancer cells fed off high-energy foods, tumours would become more aggressive and harder to treat.

This meant breast cancer patients could be helped by being given metformin, which cuts off this fuel supply to the cells.

The team looked at 219 breast cancer patients and studied which cancer cells fed on ketones and lactate, found in healthy cells.

The results, published today in bioscience journal Cell Cycle, showed that patients with cancer cells that consumed high levels of these substances were more likely to have their disease return, spread to other organs and to die.

Professor Michael Lisanti of the University of Manchester’s Breakthrough Breast Cancer Research Unit said: “We’ve shown that the saying, ‘you are what you eat’ holds true for cancer. The food cancer cells consume is crucial to how well a patient does and what treatment they need.”

The unit’s director, Professor Anthony Howell, added: “It is encouraging that some of those treatments might already be in the doctor’s drug cabinet, and cheap to prescribe. We have some way to go but we hope that drugs like metformin will be saving lives of breast cancer patients over the next few years.”