For men with metastatic prostate cancer, understanding ones prostate specific antigen (PSA) kinetics is important. Despite the issues we hear surrounding the PSA, it is still the best measure you have in aiding you in the assessing your possible outcome prognosis. PSA kinetics also are a potential surrogate marker for clinical trial results.
In most instances, quick PSA doubling time joins with a rapid alkaline phosphatase doubling time as a negative prognostic indicator.
Most clinicians agree that a 50% PSA decline is a very useful surrogate endpoint signaling a positive treatment result. Multiple studies have demonstrated that survival is almost uniformly better in men who have a greater than 50% PSA decline. Since PSA is driven by the androgen receptor, the utility of a PSA decline is probably more effective when you are taking an androgen receptor targeted therapy like bicalutamide (Casodex) or enzalutamide (Xtandi), however it still has utility when you are on other therapies.
However, you should not be confused by the two exceptions to this rule.
First, men receiving radium-223 (Xofigo) need to remember that the treatment is administered based on palliation and schedule, not on PSA measures. Also, radium-223 should be administered along with the standard of care, or other therapies, as it was in the phase III clinical trial. Therefore, in men taking Xofig if the PSA rises, it is not a definitive sign that radium-223 therapy is not effective, but it might be indicating the other co-therapy is not working. Despite this, many men do report a significant PSA decline specifically from the radiun-223 treatment.
The second exception is in men receiving sipuleucel-T (Provenge) . As with all immunotherapies, in the clinical trials for sipuleucel-T, which did demonstrate a survival benefit, there were no discernible changes in PSA levels and in many instances the PSA actually rose during the treatment. As hard is it is, you and your doctor should not pay much attention to PSA measures when having sipuleucel-T.
PSA kinetics are vital. They allow us, other than with a few exceptions, to monitor our prostate cancer’s progress and to also monitor the efficacy of our treatments.