I think it depends on how it's presented and one's ability to take a joke. For example, South Park had the episode "Breast Cancer Show Ever" and it aired when my mother was a few months out from losing her personal battle to the disease, so it would appear I would be a prime candidate to be offended by the episode. Instead, I found it to be very amusing and was laughing out loud at Cartman's joking and Wendy's reactions to it.
I think overall it takes a certain type of person to deeply enjoy shows like Family Guy and South Park, and those people HAVE to have a somewhat thicker skin and openness to parody even on taboo subjects.
And, I'm sure I'll get some flack for this, but was there some Cancer jokes on this most recent Family Guy that I'm not aware of? I guess I was too busy laughing at the Dragon's Lair joke and the "milking" of the mentally damaged horse.