My mother just turned eighty, and has signed a Living Will, stipulating NO "heroic action" be taken to keep her alive if her life is ending. She has no wish to exist hooked to a machine. My sister and I will follow her desires. Mom's health is failing, so it is only a matter of time. I am her primary care-giver at this time. She would never consent to chemo/radiation if she were diagnosed with cancer. But it's severe COPD that is killing her now. Too many decades spent smoking. Same thing got Dad three years ago.
My best friend just lost his second wife, to cancer this time. She had been in Stage Four for some years, so it was not a surprise. It had gotten into her bones, causing great pain. She endured years of chemo and radiation treatments. We have seen what tat does to cancer victims.