According to clinical statistics, people with lung cancer stage 3 will have life expectancy of 15 months.
stage 3 is divided into stage 3A and stage 3B. For stage 3A non small cell lung cancer, about 19 to 24 out of every 100 people diagnosed will live for at least 5 years. For stage 3B, around 7 to 9 out of every 100 people diagnosed (7 to 9%) will live for at least 5 years.
Although we consider statistics for life prognosis in lung cancer patients, still, no statistics can tell the patient what will happen to her/him.
Everyone's cancer is unique. The same type of cancer can grow at different rates in different people.
Prognosis depends on stage, histological type of cancer, and the patient's general well-being.
Since the diseases is in its extensive stage, and the surgery can't be performed chemotherapy and radiotherapy are treatment of choice.
It is good to know that the most common type of lung cancer, non-small cell lung cancer is generally resistant to chemotherapy or radiotherapy.
That's why chemotherapy provides only modest survival benefits (1 to 2 months) in disseminated non-small cell lung cancer.

Best wishes!
Marija