Not cancer, but MIL was "kept alive" for the last 6 months at over $100,000 in costs, she paid nothing because of Medicare and good medigap. It was sad, but she was one to refuse to accept the inevitable and kept saying "all I need is some physical therapy." Which she never really engaged in. Over the last six months spent less than 6 weeks not in residential therapy or hospital. Or hospice. Where she went three months before she passed.
What's interesting is that when sent to hospice, was given 3-4 days. Hers had been a constant series of pneumonia, C Diff, UTI, and continuing congestive heart failure. When got to hospice she perked up with the lovely surroundings. After 4 weeks they kicked her out she was doing so well. Went back to res rehab, followed by hospital, and finally died 8 days later. She always spoke well of hospice, and did well there. I'm convinced the simple fact that it was pleasant and not institutional helped her "recover." Of course, the underlying deterioration caught up with her.
My mother had stage 4 lung cancer and went through surgery, it was awful. Two weeks later they confirmed it had spread all over, died about 4 months later in our home with hospice.
My takeaway is that when confronted with the inevitable, I hope to have the sense and courage to accept it and make the most of the time I have left. Unless there's a good chance (better than 25%?) of full recovery, I hope not to engage in a lengthy battle against the inevitable. I respect others may have different views, as they say, YMMV.