Doctors don't completely understand why some people respond better to treatment than others, but overall health, emotional wellbeing and fitness levels may play a roll, Chabot says.
"It's pretty clear to me that patients who are in better health when they began treatment generally do better," he says.
But looking healthy can also be misleading.
"It's very common for patients to look awfully good, even in the face of advanced cancer," Fisch says. "This can happen because sometimes those folks are incredibly vulnerable, and they try especially hard to look good."
They may pay special attention to their appearance in order to preserve their dignity in the face of illness. When they walk into his office, Fisch says his patients may look healthy and shake his hand, but when he asks them how they are feeling, their words may tell a different story.
So as for Swayze's looking good in the airport earlier this week, Chabot says, "It's better than looking bad in the airport."
But he adds: "That's not a solid piece of information to base anything on."