Hi, I am 41 (actually my 42nd birthday is today, as it is after midnight my time!) and I was diagnosed with stage IIIC breast CA this June. Thats one step away from Stage 4, it was in 11 lymph nodes but no other body part thus far. I will tell you what my oncologist told me. Dont think about statistics, or prognosis. If it is YOU who has cancer, then you have a 50/50 chance, either it will metastacise or it wont, either you will fight it or you won;t, either you will live or you wont, you get the picture.
I believe at least 80% of the battle is mental and spiritual. My cousin, who is much older than your sister, was diagnosed with advanced lung cancer and told she had maybe a year. She is now in remission, and doing great, and that was about 5 yrs ago. Sometimes you beat the odds.
Having said that, my mom was diagnosed with breast ca at age 54, and before she died 5 yrs later, it was in her lungs, lymph nodes of the neck, spine and base of the brain. She did well until the last 2 months, when her lungs became so congested with fluid that it made breathing difficult. She did have some pain from the bone mets, but she handled pain much better than the difficulty breathing. Ive never seen anyone fight harder to live than my mom. The only reason I am telling you this is, we as a family just knew when she reached a point where only hospice care was appropriate, there was no guesswork to it. And cancer care has come such a long way in the yrs since she died, it amazes me. From diagnosis to treatment, to management of side effects, to pain management, to end-stage palliative care, it has improved drastically.
Tell your sister I am praying hard for her. I have 6 kids, from ages 17-5, and I know the fear of thinking that I wont get to see them finish school, or have babies, etc. I hope we both are on God's "miracle" list...