I have been assured by several Oncos that cancers can cause blood clots. And of course chemo can also do the same.
Mentioning P.Ca. treatments I wonder if they are solely referring to DES as an HT treatment which of course was a bit notorious for blood clots and needs an adequate blood thinner. It went out of favour as a treatment for a while for this reason.
Any form of HT reducing testosterone will affect the system, including heart muscles. Perhaps the changes to heart pumping pressure have bearing ? And we all get older so more can start to fail.
Thing to remember is that you can have DVTs without having P.Ca.
And if any risk is noted by hospitals, after ops it is often a month of blood thinning injections sometimes followed by Warfarin etc. for a while or even for life.