My father is 78 years old and has had angiosarcoma (blood vessel cancer) for three years. He received FIVE different types of chemotherapy. The very first one really helped, but the oncologist "wasn't satisfied" with results and wanted to try other ones. Not a good thing. The last combination chemo nearly killed him. He could not eat, lost several pounds, needed repeated blood transfusions (he has a pre-existent anemia), and slept all the time. It was awful. When the oncologist said "I really have something I think can help him out," my father along with my mother and my siblings said "No thanks." Enough was enough. We're talking QUALITY of life, not quantity and my father is doing as well as can be expected at this point in time.
My father also has diabetes, Parkinson's disease, and now Parkinson's dementia, along with the anemia. I think he has enough to deal with and chemo would only make him worse off than he is right now. He regained the 10 lbs, is eating very well, and NEVER complains. He doesn't feel sorry for himself either. He is a 12 year colon cancer survivor too. He has endured more than most people do.
I asked the dermatologist who diagnosed his angiosarcoma when doctors say enough is enough regarding their patients care. She said they must do everything humanly possible before telling a patient that. Sometimes I don't think that happens. I think doctors have their "quotas" and protocols to deal with. They've got grants and other money coming in to help with research and clinical trials. I think they forget about the patients and deal with stats. It's not fair. My dad's oncologist was upset when he refused more chemo, then said "You've endured so much. I can't blame you."
Personally, I think you know in your heart when you've had enough. Bottom line is quality of life.
I wish you and your family lots of luck and pray for all families dealing with cancer.