Hi again, Ed,
High Gleason does not mean high PSA. Conversely, high PSA does not mean high Gleason. PSA assays are a mesurement of an protien enzyme that originates in the prostate gland and leaks into the blood stream. This can be for varying reasons. For unknown reasons, some patients secrete more PSA than others. One factor I have heard, is if the tumor is closet to the outside of a prostate or a blood stream, even low Gleasons can emit high PSA's when in larger tumors.
I have met guys with Gleason up to 10 at diagnosis, but their PSA was below 4. After surgery, the cancer was contained within the prostate, but because of the aggressive tumor, they were still listed as high risk of relapse. PSA's need to be broken down as to what they were before treatment. Less than 10 will indicate a contained disease in most cases. But strangely, some gleason 6's can escape the prostate and still be below 10 where that is less likely for a Gleason 10 that escaped a prostate.
You will see some guys over time that have as low as Gleason 6 or 7 but PSA's over 100, or even over 1,000. Once the cancer has spread outside the prostate and tumors begin to grow elsewhere, then PSA's tend to skyrocket. There is more correlation between the size and amount of tumors than there is Gleason grade.
That is why it is said that PSA is a surregate for disease progression more so than the grade of the tumors.