What Is The Life Expectancy Of A Person With Stage 4 Cancer In Lungs, Liver And Brain?

My best friend has been in a battle with stage 4 lung cancer since Sept 2013. I am surprised she has survived this long and in relatively good health. Today her doctor told her it was in her liver, pancrease, and brain. We are afraid to ask how much time she has but from your experience what is the norm. She has started having headaches and seeing colorful spots