David -
As a fellow Vietnam vet, I've had no Parkinson's symptoms, but your question intrigued me. So I did some googling on the topic of having two significant diseases at the same time (likelihood of this, etc.). What I came up with was the term "coinfection." Googling
define coinfection
produces: "... the simultaneous infection of a host by multiple pathogen species."
So of course the next step was to google
coinfection parkinsons prostate
which produces a number of hits. One article in particular which I found and looked at was informative:
"Is There a Link Between Prostate Cancer and Parkinson's?"
From this article:
"There have been studies demonstrating an association between having PD and an increased likelihood of developing prostate cancer." (Although you seem to have gone in the opposite direction?)
"Researchers identified people diagnosed with melanoma or prostate cancer and found that they were also at a significantly increased risk of death from Parkinson’s disease."
And, interestingly, it adds: "PD and cancer seem to have opposite effects on cells. PD degenerates nerve cells and cancer causes cells to grow out of control."
But then it goes on to say that no one understands yet why there may an association, that it may be genetic and/or environmental, and that "further research is needed."
The article:
/prostatecancer.net/clinical/link-prostate-cancer-parkinsons/So you might like to start with a look at this particular article, then google as I did above, and maybe get more information from the other articles, most of which seem fairly recent.
So apparently some degree of association between PCa and PD has been suggested, and researching this may prove useful.