My mom is 50 years a old and has been recently diagnosed with stage 4 lung cancer. what is life expectancy?

Can't be certain : There are many variables that affect survival. The lung cancer type and location. Younger people tend to live longer than older people with lung cancer. Women with lung cancer have a greater life expectancy than men with with lung cancer. Every case is different. That being said, the median stage 4 non-small cell lung cancer life expectancy is about 8 months. Five year survival is only 1%.