Although I find it strange, you hear this kind of thing a lot. I've seen two cases of cancer in my immediate family. Both survived, but there wasn't a lot of fighting involved. They both got diagnosed, had an operation, and it turned out that the cancer hadn't spread. Competent surgery? Yes. Luck? Yes. Fighting? No.
I am aware, of course, that many people go through chemotherapy, and that this isn't exactly a fun experience. But still, suffering does not equal fighting. The closest thing to fighting in this context I can think is visualization. As you probably know, there is an idea that you're supposed to imagine little Pac-Man-type creatures moving through your body, eating up cancer cells. If that works, I'd like to see a solid study on it - I'm envisioning a large randomized controlled trial analyzed using IV techniques. Even if it does work, visualization doesn't strike me as particularly fight-like.
You might say that even if it's nonsense, it is nice to think of people who have been through hard times, often due to no fault of their own, and came through, as strong, and admire them for it. O.k. But there's a flipside to that. It suggests that those who didn't pull through sorta had themselves to blame - they just weren't tough enough. That seems kinda wrong.