• The promising ‘seek and destroy’ treatment uses highly specific radiation doses
• But it doesn’t work for all men – this test could make it easier to check 
• Experts hope the therapy could benefit more than 5,000 men a year in the UK
• The eligibility test looks for a genetic fault linked to a certain type of tumour 

By SAM BLANCHARD SENIOR HEALTH REPORTER FOR MAILONLINE

A test can work out which prostate cancer patients may be eligible for a pioneering ‘seek and destroy’ treatment.

Researchers last month revealed they had found a way to accurately guide powerful radioactive molecules directly to prostate tumours.

But the promising therapy doesn’t work for everyone – and this new test will make it easier to spot the men for whom it may be effective.

The team of scientists developed the test to see whether prostate cancer patients have a problem with their DNA which stops it repairing itself.

This is linked to how much of a protein called prostate-specific membrane antigen (PSMA) someone has, they found.

Higher amounts indicate the treatment may be suitable because it is these PSMA proteins which the treatment targets, so more of them gives it more targets.

This means men with the error may be prime patients to test it on, according to the team at the Institute of Cancer Research in London.

They said the genetic test could be used as a first screening test to work out which patients should be given the radiotherapy.

‘We found that testing for DNA repair defects was a good indication of which tumours had high levels of PSMA – and so would be expected to respond to these PSMA-targeted therapies,’ said Professor Johann de Bono.

‘We will need to further assess the use of DNA tests to target these treatments effectively in routine care.

‘But we can already now start to take into account DNA repair faults in our design of clinical trials.

‘Our new study helps to explain why some patients respond to search-and-destroy treatments and others don’t.

‘Understanding the biology of response to these new treatments is critical to getting them into use in the clinic as soon as possible.’

The researchers are now planning to trial the treatment, which works by aiming destructive radiation particles at cancerous cells.

These deliver a powerful shot of radiation to tissue 1mm around it, destroying the cancer but avoiding the collateral damage caused by traditional radiotherapy.

Current radiotherapy risks damaging healthy tissue around the prostate, which can cause debilitating side effects such as incontinence or erectile dysfunction.

PSMA radiotherapy is being tested in 10 trials around the world and its developers say it could help at least 5,000 British men each year if the NHS started using it.

Professor Paul Workman, chief executive of the ICR said: ‘PSMA-targeting drugs are an exciting new wave of treatments coming through for prostate cancer.

‘They combine a potent nuclear medicine with a “homing signal” that searches out prostate cancer cells.

‘To get these new drugs into the clinic, we need a good understanding of the biology of the treatment response and how to spot those patients who will most benefit.

‘This new study gives us an important handle on how to select men for treatment.’

The research was published in the journal European Urology.