Obviously outright lying is not okay, but I wouldn't feel guilty about the hope part. With the roller coaster my dad and our family rode off and on for about four years, the doctors commented about how his attitude in regards to not giving up helped keep him from unknowingly self-sabotaging. Sort of a "help me, help you" effect that enabled him to communicate better, keep a level head about his options, and allowed him to be considered as a candidate for some of the more advanced procedures and methods. For a guy who wasn't supposed to make it through the night back in 2001 when one hospital mistook the two liver tumors nobody realized he had - and one of which had apparently burst - for kidney stones until they realized he was in liver failure, I wouldn't trade those four bonus years I got with him for anything.

Just remind your patients that predicting reality is no more definitive than predicting the weather. It might sound cliche, but it's sort of true. Extremely intelligent people do the best with the information they have and they will keep striving to gain more, but things change and at the end of the day, nobody knows for sure what will end up being 'real'.