From the perspective of the family, dementia is something that robs the afflicted person of his dignity and the family of the positive aspects of sharing his company, yet leaves all of the mundane burdens intact for years and years, thus causing a great deal of trauma, whereas cancer is a situation in which the entire family fights along with the person suffering from it.

From the perspective of the actual person, cancer usually strikes much earlier, involves a great deal of suffering and ends in death far too often, whereas dementia is something that slowly creeps up far later in life and, when it has hold, you don't even realize it anymore.

One grandmother died of cancer, the other of a heart attack in her sleep after several years of dementia. Which was harder on my parents? Obviously the dementia. Which would I choose for myself if I had to? Probably the dementia; there was no chemo, and even the day she died she had a nice lunch before going to take a nap from which she just didn't wake up.