I think it depends on how the indiviual takes their illness. If they are accepting of it, perhaps they have a better outlook. But if they don't accept it, I think they're more miserable than we might know.
I say this because my mom had lung cancer when I was sixteen. The doctors would always toy with her; saying how long she'd have to live if she did this or didn't do that, but as her time came near, she realized that the doctors all lied to her. One day, I remember her crying to me saying, "I'm so scared to die, I'm just so scared," because my dad would always yell and scream at her while she was on her death bed. It was heartbreaking because she knew her fate, it was coming sooner rather than later, and there was nothing she could do or think to make it any better.
I would classify my mom as the type that didn't have a better outlook, but I'm positive that that's not everybody. I believe it all comes down to the person's environment, surroundings, support system, and their own positive beliefs.