Why breast cancer drugs fail for one in four: Scientists discover that tumours can create their own supply of fuel

Scientists have made a breakthrough by discovering how the breast cancer tumours of a quarter of patients resist chemotherapy treatment.

Drugs used to ‘starve’ tumours of the hormone that helps them grow often fail because the cancerous growths create their own supply, the researchers found.

The breast cancer drugs, called aromatase inhibitors, operate by stopping the woman’s body from producing oestrogen.

Scientists have discovered how breast cancer tumours in a quarter of patients resist chemotherapy. Picture posed.

But tests showed that the tumour cells produce extra copies of genes for the aromatase enzyme which allows them to make oestrogen.

Dr Luca Magnani, from Imperial College London, said: ‘For the first time we have seen how breast cancer tumours become resistant to aromatase inhibitors.

‘The treatments work by cutting off the tumour’s fuel supply – oestrogen – but the cancer adapts to this by making its own.’

About 70 per cent of breast cancers are stimulated by oestrogen.

Another drug, tamoxifen, blocks the receptors on tumour cells that enable them to respond to the hormone.

Regardless of a tumour’s ability to create its own oestrogen, tamoxifen and aromatase inhibitors eventually stop working in about one in three patients anyway, and scientists are keen to find out why. They are trying to develop a test that can identify patients whose cancer cells are starting to produce aromatase and oestrogen.

Dr Magnani added: ‘In many cases when an aromatase inhibitor stops working in a patient, doctors will try another type of aromatase inhibitor.

‘However, our research suggests that if the patient’s cancer has started to make aromatase, this second drug would be useless. This is why we need a test to identify these patients.’

In the study, published in the journal Nature Genetics, tumour samples were taken from 150 women whose breast cancers had returned and spread. All the women were treated at the European Institute of Oncology in Milan, northern Italy.

Tests show breast cancer cells are able to produce their own supply of hormones making them resistant to drugs that work by trying to stop them producing their own oestrogen.

Dr Richard Berks, of the charity Breast Cancer Now, said: ‘This reveals a new way that the most common breast cancers can survive anti- hormone treatments.

‘By producing more aromatase, breast tumours could resist treatment and return elsewhere around the body, years or even decades after the disease first appeared.

‘Once breast cancer spreads it sadly becomes incurable, so we urgently need to tackle drug resistance.

‘It is critical we find ways to spot, at an early stage, whether a person’s breast cancer is becoming resistant to treatment so that they can be moved on to more effective options.