I have to share a pet peeve of mine. I know people mean well when they tell cancer patients that "attitude is everything." No, it's not! Life isn't fair, and sometimes the sunniest, healthiest, sweetest people you know will get cancer. And when they do, they might be joyful in all things most of the time, but cancer will get you down sometimes. PLEASE! Let them have that down moment.
It's really placing an unfair burden on someone who is scared, may be in pain, and who may be trying to simply maintain under a regimen of chemo or radiation, or both. And how about someone who HAS been cheery and is still in the last stage of life? How do you think they feel?
I suggest a hug and a few words about the fact that you care for that patient, and they have been in your prayers. Unless you've been in their shoes (I have), you really DON'T know how they feel. Trust me on this.