What is the average life expectancy for patients diagnosed with non small cell lung cancer stage 4?

Not great . Less than 10% of patients survive past 5 years. Average life expectancy is about a year on average.
Very low-5% 5 yr. . Stage IV non-small cell lung cancer is metastasis to any site other than lung, like brain. This has a very low 5 year survival of 5% or less. Very few (about 20%) have localized dissease at diagnosis.