PSA Monitoring

PSA is arguably the most effective tumor marker in all of oncology during and after treatment of prostate cancer, but it is not the only test available for evaluation of the risk of prostate cancer.  A single PSA blood test is of limited value in detecting prostate cancer.  But, longitudinal assessment of PSA showing a very low or stable PSA may be the most reassuring finding that prostate cancer is not present or progressing for an individual patient. False positive results can occur with the PSA blood test, because prostate specific antigen (PSA) protein levels can increase with benign enlargement of the prostate or infection.  However, we use PSA monitoring as only a first step in following men.

Abnormalities of PSA are evaluated further with secondary tests for prostate cancer, including the 4k Score test or ExoDx, that are more specific for the presence of prostate cancer.  Why not just use these additional tests?  The tests (PSA, 4k Score, ExoDx) are complementary to each other.  For example, the 4k Score test can provide an estimate of the risk of prostate cancer (the test is reported as a % risk of prostate cancer being present), but the 4k Score test does not take into account the stability of PSA.  So, even if a modest risk of prostate cancer was predicted by the 4kScore, a man with stable and low PSA would have neglibible risk of clinically significant prostate cancer. 

ExoDx is based on a simple urine sample, where the test analyzes the contents of exosomes, particles released by all cells.  For ExoDx, an analysis of nucleic acids within the exosomes (specifically ERG, PCA and SPDEF RNA) to predict the chance of clinically significant prostate cancer (Gleason Grade > 7; which may require treatment) for a patient.  A level greater than 15 is considered a positive (abnormal) test suggesting an increased risk of prostate cancer.

For men with an abnormal prostate evaluation, an MRI of the prostate can provide additional structural information on the risk of, and site(s) of possible cancer within the prostate.  MRI studies are reported with the presence or absence of lesions, as well as the chance of prostate cancer being present within that lesion(s).  The reporting is done with a PIRADS score, ranging from 1-5.  PIRADS 5 lesions have a high risk of prostate cancer being present (usually 90-95%).  PIRADS 4 lesions have a 60-70% risk of prostate cancer, and PIRADS 3 lesions are considered equivocal findings. 

Detection of prostate cancer requires a biopsy of the prostate.  Prostate biopsies have historically been done with an ultrasound-guided approach going through the rectum.  Such an approach was associated with a moderate risk of sepsis (infection) after the biopsy procedure.  We have now modified this approach to prostate biopsy so the biopsy is done by passing the biopsy needle directly through the skin into the prostate, rather than through the rectum.  This approach almost eliminates the risk of infection after biopsy maintaining the effectiveness of prostate cancer detection.  The MRI findings are key for guiding a prostate biopsy, so this test is almost always done prior to a biopsy.  Prostate biopsies routinely sample all areas of the prostate, but any lesion of concern on MRI is a site of emphasis for prostate biopsies.

My approach to management of PSA monitoring and evaluation of an abnormal PSA is also summarized in this video: https://youtu.be/scncDuP3dvM?list=TLPQMjEwOTIwMjP1bcMbSy7Ktw