This is kind of a scary story, but I think it should be told here.
When my mom was first hospitalized, the onc. at the small hospital thought she had pancreatic cancer due to the met there. With spread to the lungs, it would have been Stage IV...if you think lc stats are grim, take a look at pancreatic cancer. Moves fast and has very little respect for chemo. My mother's oldest sister died of PC about 10 years ago, and it does seem to have a hereditary tendency.
The onc. explained that with the lung tumor, my mom could hemorrage, and there was a 50% chance of it being fatal. He told us that if she were intubated for a fatal hemorrage, it could not be removed. Mom signed a DNR.
Then the pulmonologist told mom he thought it might be lung cancer. Mom had to have a stent placed to open her bile duct (jaundice is what sent her to the hospital), and brushings were taken to try to get a dx. No luck. She was scheduled for a needle biopsy of the pancreas, but the tech backed out at the last minute, saying he was not comfortable reaching the tumor location. So the pulmonologist suggested a bronchoscopy.
During the procedure, Mom bled from the tumor and had to be intubated. Mom and Dad had revoked the DNR for the procedure. The hospital staff was not very encouraging about Mom's prognosis that awful night in ICU. One dr. was trying to prepare my dad for the possibility of her not making it. But she proved to be quite a fighter - and really tough to keep sedated . A few days later, she was stabilized and taken off the ventilator.
And now, 5 months later, she's NED and ready to undergo testing for stem cell supported therapy. If Mom had not resisted keeping the DNR...I don't even want to think about it.
So if someone doesn't want to sign a DNR, let it be the patient's choice. Sometimes crisis points happen which can be overcome, even when the disease is progressing. I'd think long and hard about a DNR for anyone in my family, because I've seen first-hand how even when something goes wrong, it may not be as bad as you think.