LONDON - Men with advanced prostate cancer are often prescribed drugs to stop testosterone fuelling the growth of the tumour's cells. These treatments are effective, but the cancer can become resistant to it over time.

Now, in a significant breakthrough, scientists have worked out what is causing this resistance – and how to reverse it. It turns out that when deprived of testosterone, the cancer cells "hijack" white blood cells called myeloid cells, pulling them into the tumours and turning them into hormone factories.

In an effort to counter this, 21 men whose cancer had stopped responding to drugs were given an experimental treatment that prevents myeloid cells from being drawn into tumours, along with enzalutamide, a conventional treatment.

A quarter of the participants responded to the new regimen; their tumours shrunk by more than 30%, and they showed "dramatic" reductions in their levels of prostate-specific antigen (PSA), which is often a marker for the disease.

The hope is that pharmaceutical companies will now work on developing drugs that are even better at combating resistance, said Prostate Cancer UK, one of the study's funders.