New screening method could identify men at risk for prostate cancer
The standard prostate cancer screening test – the PSA, or Prostate Specific Antigen test – uses blood samples to measure the levels of a man’s PSA, a protein which can be elevated if the patient has prostate cancer – or other, non-malignant prostatic conditions such as an enlarged prostate gland. According to Arul Chinnaiyan, director of the Michigan Center for Translational Pathology in Ann Arbor, ”Most men with elevated PSA levels don’t have prostate cancer.”
A new method of screening which uses urine instead of blood to check for prostate cancer markers could better predict whether a man has or could have prostate cancer, as well as the severity of the disease.
The test detects two prostate cancer-specific biomarkers: TMPRSS2:ERG, which is detected in roughly 50 percent of prostate tumors using standard PSA testing - and PCA3, a highly sensitive marker found in high amounts in over 95 percent of prostate cancers.
The study involved 1,065 men whose screenings showed elevated levels of PSA; the men were stratified into low, intermediate and high score groups. Using biopsies, prostate cancer was confirmed in 21%, 43% and 69% of the respective groups. Results can be found published in Science Translational Medicine.
Researchers say that men in high risk groups should get biopsies, as well as men whose biopsy is negative but have a high scoring screening test. In addition to helping detect the presence of prostate cancer, high urine test scores were also correlated with determining how aggressive the cancer was, based on the tumor size and the Gleason Score, which biopsies alone cannot do.
The San Diego, California-based molecular diagnostic company, Gen-Probe, licensed the test and sought FDA approval.
“This is one big step towards better risk assessment for individual patients,” says Jack Schalken, director of research in the urology department at Nijmegen Centre for Molecular Life Sciences in the Netherlands. It is also a significant move towards the goal of personalized medicine, he says, as different subtypes of cancer are likely to require different treatments. “Clinicians are sitting in front of only one person; we need a way to assess how aggressive that patient’s cancer is.”
Some researchers are more cautions. According to Shiv Srivastava, scientific director at the Center for Prostate Disease Research in Rockville, Maryland, the study is ”a major advance” – but independent studies across more general populations and ethnicities are necessary to confirm if the study results are applicable to all men. Recent work by Srivastava suggests that TMPRSS2:ERG expression is different in those of African-American ethnicity.
The standard PSA test looks for a biomarker which can indicate the presence of prostate cancer, but can also fail to indicate it and can be elevated by other, benign, conditions of the prostate gland. What Srivastava and Schalken agree on is that the urine test is advantageous in that it looks for biomarkers specific to prostate cancer.
The next big thing?
Despite their apparent advantages, urine-based prostate cancer tests do not appear poised to replace the standard blood-based PSA test just yet. Says Chinnaiyan, ”We are initiating long-term, prospective trials to begin gathering enough data to determine whether this test could, one day, serve as a replacement. ”But the bar will be pretty high when attempting to replace a test physicians have used for so long.”