Have you ever tried another bicycle saddle? The pressure of saddle on the prostate is known to raise the PSA. A wider saddle or a saddle with a cut-out could help.
I can give you my experience. I had a PSA reading in June of about 7, which was up from 4 the previous year. I had another test in October and it was 10.4, so my doctor sent me to a urologist who gave me a biopsy, which was positive for prostate cancer on the right side of my prostate, Gleason score 4/3, and recommended either surgery or radiation.
I'm currently awaiting surgery, which will probably take place either at the end of December or beginning of January. Yesterday I had another PSA test, and the result was 9.06. So yes, it's possible for it to go down if you have prostate cancer.
As embram said, it’s possible for it to drop, but that’s because there are other factors besides prostate cancer that can affect PSA - recent sexual activity, inflammation from BPH or prostatitis, even bike riding because of the pounding that area takes. However, LONG-term it would most likely continue to rise as the cancer grows & spreads.
I’m a prostate cancer patient myself, had surgery Jul 2018 (PSA was 9.2 pre-surg) and unfortunately, PSA did not drop down to undetectable afterward, continues to rise & is now 3.08, will need further treatment. They want me to do hormone therapy, which would drop my Testosterone down to near zero, causing a lot of unwanted side effects, which I don’t want. Have a tough decision to make very soon, can’t put it off much longer...
Anyway, good luck w/ future diagnosis & treatment...