A new saliva test that can identify men at high risk of prostate cancer is undergoing pilot trials at GP practices in London.
Scientists will assess whether advice or preventative treatment can reduce cases of the disease among those men who are singled out.
The groundbreaking study follows research linking single-letter changes in the genetic code with a six-fold increased likelihood of developing prostate cancer.
By looking for these DNA defects, scientists were able to identify the 1% of men at highest risk.
Lead researcher Professor Ros Eeles, from the Institute of Cancer Research in London, said: "If we can tell from testing DNA how likely it is that a man will develop prostate cancer, the next step is to see if we can use that information to help prevent the disease."
A spokesman for the Institute confirmed that a pilot study involving 300 patients had now been launched at three London GP practices, one in the north of the city and two in the south.
Saliva samples taken from participants will be tested for the rogue DNA variants.
Once the initial trial has been completed, the study will be expanded out to 50 surgeries across the London area.
For the groundwork research, reported in the journal Nature Genetics, the scientists used DNA from blood samples.
They compared around 500,000 single-letter changes in the genetic code of nearly 80,000 men with prostate cancer and more than 61,000 who were free of the disease.
In total, 63 new genetic variants that increase the risk of prostate cancer were identified.
Combining these with 100 others that were previously known made it possible to single out men nearly six times more likely than average to develop prostate cancer during their lifetime.
Many of the newly discovered variants affected genes that help regulate communication between immune system cells and other cells in the body.
This implies that broken immune system pathways play a major role in prostate cancer, which in turn could have important implications for immunotherapy treatments.
Each year around 47,000 men are diagnosed with prostate cancer in the UK and 11,600 die from the disease.
Prof Eeles said: "By looking at the DNA code of tens of thousands of men in more depth than ever before, we have uncovered vital new information about the genetic factors that can predispose someone to prostate cancer, and, crucially, we have shown that information from more than 150 genetic variants can now be combined to provide a readout of a man's inherited risk of prostate cancer."
Professor Paul Workman, chief executive of The Institute of Cancer Research, said: "We are on the cusp of moving from theory to practice - from explaining how genetics affects prostate cancer risk, to testing for genetic risk and attempting to prevent the disease."
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