The situation with my mother was she had a large bladder cancer. I went with her to the oncologist and he explained very clearly the likely benefit, which seemed pretty marginal. When I said it didn't seem a good idea, he agreed it was the right decision. Its not something I like to talk about much, because she only died last year.
I do find that the patients I have treated that are under the oncologists, do seem to have an overoptimistic view of their outlook. Whose fault that is I don't know.