Some people can be cured of stage 4 lung cancer depending on where it has spread.
When the lung cancer spreads and becomes stage 4 lung cancer it makes it harder to cure and you have less chance of surviving the stage 4 lung cancer and having it cured.
If the lung cancer is diagnosed soon enough before it becomes stage 4 lung cancer then in most cases the lung cancer can be cured.
The longer the lung cancer is left to spread through your body the less curable it becomes.
Still there's treatment and a slight chance that you may be cured of it or at least slow the lung cancers progress so that you do not die as quickly.
But if you do get diagnosed with stage 4 lung cancer you can expect to die within 5 to 10 years after diagnoses but sometimes sooner.
Then again there could be a chance of survival.
But there's no guarantee that you will live and be cured of it.