Usually symptoms of lung cancer do not appear until the disease is already in an advanced state, and has spread. Sometimes, people are lucky, and an early stage lung cancer is discovered due to tests for other conditions. (This happened to the mother of a friend of mine; her lung cancer was diagnosed when she underwent a chest x-ray prior to hip surgery. The tumor was removed, and she lived for  many years thereafter). This then, brings up the question of early screening for lung cancer.