Average 4-6 months: The average survival for patients with stage 4 lung cancer is usually 4-6 months if only supportive therapy is used.et help from a doctor now ›. Stage 4 lung Ca. : A few months, somewhere between 3 months or shorter to 8 months on average depending on the extent of disease and tumor aggressiveness. But i want to emphasize stage 4 lung cancer is not curable, but treatable.