A more accurate genetic test for prostate cancer is being developed.
Scientists have found variations in DNA that affect individual "healthy" levels of prostate specific antigen (PSA), which are used to diagnose the disease.
Currently, men with PSA levels above a certain threshold have samples of their prostate gland removed for testing.
But PSA levels can increase for reasons other than prostate cancer, and normal levels are different for every individual.
As a result many men without cancer are given unnecessary painful and worrying biopsies while others have cancers that are not diagnosed until they become advanced.
For this reason PSA testing has been criticised as a way of detecting cancer and ruled out for national screening in the UK.
The new test being developed by the Icelandic company deCODE genetics would make it possible to establish individual PSA thresholds. This in turn could allow for more accurate and meaningful screening.
The research, published in the journal Science Translational Medicine, identified six single-letter changes in the genetic code called single nucleotide polymorphisms, or SNPs.
Lead researcher Dr Kari Stefansson, chief executive of deCODE, said: "This is straightforward genetics with direct clinical utility."