Anecdotally, my mother was diagnosed with Stage 4 lung cancer (despite never smoking in her life). It had already metastasized to her brain by the time they caught it. I read the clinical literature, and she probably had about 3 months to live.

BUT: her cancer had a druggable mutation. She took Tarceva, then Tagrisso. She lived 7 years, before an aggressive lymphoma finally ended things.

The side effects were not pleasant. Her hair and skin got weird, and she had extensive digestive problems. But I am immensely grateful to the researchers who developed these drugs and allowed her to live long enough to see her first grandchild make it to kindergarten.