Pretty sure I've read in more than one place that men produce less semen as they age anyway, in which case that's going to apply to most people here, but also most people who don't have PCa, so just asking people with PCa here might give a completely wrong impression.
I also saw a couple of references to seminal vesicles storing semen produced in the prostate in this thread, which I think is wrong. My understanding (which also might be wrong!) is that both the seminal vesicles and the prostate produce different constituents of the semen. The seminal vesicles produce the thicker white milky component which they store for use, and the prostate produces a clear liquid (mainly on demand rather than stored), which amongst other things, causes the thicker component from the seminal vesicles to liquify and become less milky some minutes after mixing during ejaculation. If you ejaculate more than once, it tends to get more watery each time because the seminal vesicles will have run out and take a longer time to replenish, but the prostate can quickly make it's clear constituent again.
I do recall having small jelly-like lumps in my semen for some years, more if I hadn't ejaculated for some days, and I did ask about it, but was told it was not uncommon. However, I think it probably went away a decade before being diagnosed with PCa, so not obviously related. My seminal vesicles are clear of cancer.