There is a super depressing story of a YouTuber named Leathersmokemi who died engaging in a similar fetish. Nick Crowley did a good video on him. I don't know of a fetish centered on prostate cancer specifically but there are cancer fetishists and the fetish centered on terminal illness is called nosaphillia so it's certainly possible that there are fetishists already out there focused on prostate cancer specifically.
Prostate stimulation is sexy not because of the prostate itself but because it is incredibly sensitive and pleasuring when stimulated, which in turn is of course sexy for those who like to please their partner and are maybe also into butt stuff.
It's probably because a huger number of prominent secondary sexual sex characteristics get fetishized.
A brief search seems to show that it's an attractive quality like masculine forearms, and has a degree of fetish amongst the strangulation fetish community.