Often, even after treatment/surgery, prostate cancer leads to cancer in another part of the body, like bone cancer, which is a slow, horrible, painful death. I knew of a case like that, and am just saying that this might be a possibility, and if so, Mr. Sherman might have decided to take matters into his own hands, making sure that he and his wife did not have to go through that. I hope I am wrong.
It also seems to me that because of his wealth and influence he could have had many enemies. Very high level assassins for hire can I have read, move like ghosts, and leave the impression of suicide or accident, when in fact, it was murder. Even if he, or she did have cancer, the possibility that they might have made changes to wills, could have also provided motives. Follow the money. Who benefits, and how ? That, and the medical evidence after autopsies, as well as forensic evidence in the house may provide answers. For the family's sake, and for justice I hope so. IMO